diff --git a/samples/Sandbox/Sandbox.csproj b/samples/Sandbox/Sandbox.csproj
index d2e66988e0..7a57a13529 100644
--- a/samples/Sandbox/Sandbox.csproj
+++ b/samples/Sandbox/Sandbox.csproj
@@ -5,6 +5,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <TargetLatestRuntimePatch>true</TargetLatestRuntimePatch>
     <IncludeAvaloniaGenerators>true</IncludeAvaloniaGenerators>
+<!--    <AvaloniaXamlIlDebuggerLaunch>true</AvaloniaXamlIlDebuggerLaunch>-->
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Avalonia.Build.Tasks/GenerateAvaloniaResourcesTask.cs b/src/Avalonia.Build.Tasks/GenerateAvaloniaResourcesTask.cs
index 264a86b014..620cd4723d 100644
--- a/src/Avalonia.Build.Tasks/GenerateAvaloniaResourcesTask.cs
+++ b/src/Avalonia.Build.Tasks/GenerateAvaloniaResourcesTask.cs
@@ -127,7 +127,7 @@ namespace Avalonia.Build.Tasks
 
         public bool Execute()
         {
-            Enum.TryParse<MessageImportance>(ReportImportance, out _reportImportance);
+            Enum.TryParse(ReportImportance, true, out _reportImportance);
 
             BuildEngine.LogMessage($"GenerateAvaloniaResourcesTask -> Root: {Root}, {Resources?.Count()} resources, Output:{Output}", _reportImportance < MessageImportance.Low ? MessageImportance.High : _reportImportance);
             var resources = BuildResourceSources();
diff --git a/src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs b/src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs
index d71070e818..d4c4ae8667 100644
--- a/src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs
+++ b/src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs
@@ -288,6 +288,24 @@ namespace Avalonia.Build.Tasks
                             if (precompileText != "true")
                                 throw new XamlParseException("Invalid value for x:Precompile", precompileDirective);
                         }
+
+                        var classModifierDirective = initialRoot.Children.OfType<XamlAstXmlDirective>()
+                            .FirstOrDefault(d => d.Namespace == XamlNamespaces.Xaml2006 && d.Name == "ClassModifier");
+                        bool? classModifierPublic = null;
+                        if (classModifierDirective != null)
+                        {
+                            var classModifierText = (classModifierDirective.Values[0] as XamlAstTextNode)?.Text.Trim()
+                                .ToLowerInvariant();
+                            if ("Public".Equals(classModifierText, StringComparison.OrdinalIgnoreCase))
+                                classModifierPublic = true;
+                            // XAML spec uses "Public" and "NotPublic" values,
+                            // When WPF documentation uses "public" and "internal".
+                            else if ("NotPublic".Equals(classModifierText, StringComparison.OrdinalIgnoreCase)
+                                     || "Internal".Equals(classModifierText, StringComparison.OrdinalIgnoreCase))
+                                classModifierPublic = false;
+                            else
+                                throw new XamlParseException("Invalid value for x:ClassModifier. Expected value are: Public, NotPublic (internal).", precompileDirective);
+                        }
                         
                         var classDirective = initialRoot.Children.OfType<XamlAstXmlDirective>()
                             .FirstOrDefault(d => d.Namespace == XamlNamespaces.Xaml2006 && d.Name == "Class");
@@ -297,8 +315,21 @@ namespace Avalonia.Build.Tasks
                             if (classDirective.Values.Count != 1 || !(classDirective.Values[0] is XamlAstTextNode tn))
                                 throw new XamlParseException("x:Class should have a string value", classDirective);
                             classType = typeSystem.TargetAssembly.FindType(tn.Text);
+
                             if (classType == null)
                                 throw new XamlParseException($"Unable to find type `{tn.Text}`", classDirective);
+
+                            var isClassPublic = typeSystem.GetTypeReference(classType).Resolve().IsPublic;
+                            classModifierPublic ??= isClassPublic;
+
+                            // We do not really need x:ClassModifier support for x:Class, but we can at least use it for validation here.
+                            if (classModifierPublic != isClassPublic)
+                            {
+                                throw new XamlParseException(
+                                    "XAML file x:ClassModifier doesn't match the x:Class type modifiers.",
+                                    precompileDirective);
+                            }
+                            
                             compiler.OverrideRootType(parsed,
                                 new XamlAstClrTypeReference(classDirective, classType, false));
                             initialRoot.Children.Remove(classDirective);
@@ -312,6 +343,8 @@ namespace Avalonia.Build.Tasks
                         var classTypeDefinition =
                             classType == null ? null : typeSystem.GetTypeReference(classType).Resolve();
 
+                        // All XAML files are public by default.
+                        classModifierPublic ??= true;
 
                         var populateBuilder = classTypeDefinition == null ?
                             builder :
@@ -319,10 +352,11 @@ namespace Avalonia.Build.Tasks
 
                         ((List<XamlDocumentResource>)parsedXamlDocuments).Add(new XamlDocumentResource(
                             parsed, res.Uri, res, classType,
+                            classModifierPublic.Value,
                             populateBuilder,
                             compiler.DefinePopulateMethod(populateBuilder, parsed, populateName,
-                                classTypeDefinition == null),
-                            buildName == null ? null : compiler.DefineBuildMethod(builder, parsed, buildName, true)));
+                                classTypeDefinition == null && classModifierPublic.Value),
+                            buildName == null ? null : compiler.DefineBuildMethod(builder, parsed, buildName, classModifierPublic.Value)));
                     }
                     catch (Exception e)
                     {
@@ -368,7 +402,7 @@ namespace Avalonia.Build.Tasks
                             document.PopulateMethod,
                             document.BuildMethod,
                             builder.DefineSubType(compilerConfig.WellKnownTypes.Object, "NamespaceInfo:" + res.Name,
-                                true),
+                                document.IsPublic),
                             (closureName, closureBaseType) =>
                                 populateBuilder.DefineSubType(closureBaseType, closureName, false),
                             (closureName, returnType, parameterTypes) =>
@@ -502,7 +536,8 @@ namespace Avalonia.Build.Tasks
 
                         }
 
-                        if (document.BuildMethod != null || classTypeDefinition != null)
+                        if (document.IsPublic
+                            && (document.BuildMethod != null || classTypeDefinition != null))
                         {
                             var compiledBuildMethod = document.BuildMethod == null ?
                                 null :
diff --git a/src/Avalonia.Themes.Fluent/Accents/BaseColorsPalette.xaml b/src/Avalonia.Themes.Fluent/Accents/BaseColorsPalette.xaml
index 362d543646..620add9045 100644
--- a/src/Avalonia.Themes.Fluent/Accents/BaseColorsPalette.xaml
+++ b/src/Avalonia.Themes.Fluent/Accents/BaseColorsPalette.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <!-- https://docs.microsoft.com/en-us/previous-versions/windows/apps/dn518235(v=win.10)?redirectedfrom=MSDN -->
   <ResourceDictionary.ThemeDictionaries>
     <ResourceDictionary x:Key="Default">
diff --git a/src/Avalonia.Themes.Fluent/Accents/BaseResources.xaml b/src/Avalonia.Themes.Fluent/Accents/BaseResources.xaml
index 517a80fd7e..6f12f1d306 100644
--- a/src/Avalonia.Themes.Fluent/Accents/BaseResources.xaml
+++ b/src/Avalonia.Themes.Fluent/Accents/BaseResources.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:sys="using:System"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <FontFamily x:Key="ContentControlThemeFontFamily">fonts:Inter#Inter, $Default</FontFamily>
   <sys:Double x:Key="ControlContentThemeFontSize">14</sys:Double>
 
diff --git a/src/Avalonia.Themes.Fluent/Accents/FluentControlResources.xaml b/src/Avalonia.Themes.Fluent/Accents/FluentControlResources.xaml
index 61a74f26a4..397f7ec431 100644
--- a/src/Avalonia.Themes.Fluent/Accents/FluentControlResources.xaml
+++ b/src/Avalonia.Themes.Fluent/Accents/FluentControlResources.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ResourceDictionary.ThemeDictionaries>
     <ResourceDictionary x:Key="Default">
       <!-- Resources for Button.xaml -->
diff --git a/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj b/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
index e63a0c9c26..660661fc94 100644
--- a/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
+++ b/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
-    <!-- NativeMenuBar uses ReflectionBinding -->
-    <NoWarn>$(NoWarn);IL2026</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/AdornerLayer.xaml b/src/Avalonia.Themes.Fluent/Controls/AdornerLayer.xaml
index c4b91b4822..fefa1ea055 100644
--- a/src/Avalonia.Themes.Fluent/Controls/AdornerLayer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/AdornerLayer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Thickness x:Key="SystemControlFocusVisualMargin">0</Thickness>
   <Thickness x:Key="SystemControlFocusVisualPrimaryThickness">2</Thickness>
   <Thickness x:Key="SystemControlFocusVisualSecondaryThickness">1</Thickness>
diff --git a/src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml b/src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml
index 2113ae4cb0..228aeaad17 100644
--- a/src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:generic="using:System.Collections.Generic">
+                    xmlns:generic="using:System.Collections.Generic"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <AutoCompleteBox Width="200">
diff --git a/src/Avalonia.Themes.Fluent/Controls/Button.xaml b/src/Avalonia.Themes.Fluent/Controls/Button.xaml
index 126f2c22e0..6c6ca967e7 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Button.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Button.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml b/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
index 3ce4730698..095e801d0c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ButtonSpinner.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:sys="using:System"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml b/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
index 9c66ea9b84..2f4a444529 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <Calendar />
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
index 76b51ca819..206973b7ee 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
@@ -5,7 +5,8 @@
 // All other rights reserved.
 -->
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
index 2a3496b648..4739a5b9c5 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Margin="20, 20, 20, 200">
       <CalendarDatePicker Width="200" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
index 6a57cfacd0..904a234ada 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
@@ -5,7 +5,8 @@
 // All other rights reserved.
 -->
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
index 7276742e7d..3bbef81695 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
@@ -6,7 +6,8 @@
 -->
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:sys="using:System">
+        xmlns:sys="using:System"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <Calendar DisplayDate="2000-01-01">
diff --git a/src/Avalonia.Themes.Fluent/Controls/CaptionButtons.xaml b/src/Avalonia.Themes.Fluent/Controls/CaptionButtons.xaml
index 0180c3f395..41d74c6063 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CaptionButtons.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CaptionButtons.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/Carousel.xaml b/src/Avalonia.Themes.Fluent/Controls/Carousel.xaml
index 91e331693e..b94ef9b5d9 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Carousel.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Carousel.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Carousel}" TargetType="Carousel">
     <Setter Property="Template">
       <ControlTemplate>
diff --git a/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml b/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
index 28f8649e2d..fc0a8c7c66 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ComboBox.xaml b/src/Avalonia.Themes.Fluent/Controls/ComboBox.xaml
index bc36ad987e..18bf01ece7 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ComboBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ComboBox.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="10">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ComboBoxItem.xaml b/src/Avalonia.Themes.Fluent/Controls/ComboBoxItem.xaml
index 581cbaf80a..ea55770a51 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ComboBoxItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ComboBoxItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <Border Background="{DynamicResource ComboBoxDropDownBackground}" BorderBrush="{DynamicResource ComboBoxDropDownBorderBrush}" BorderThickness="{DynamicResource ComboBoxDropdownBorderThickness}" Margin="0,-1,0,-1" Padding="{DynamicResource ComboBoxDropdownBorderPadding}" CornerRadius="{DynamicResource OverlayCornerRadius}">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ContentControl.xaml b/src/Avalonia.Themes.Fluent/Controls/ContentControl.xaml
index 4caf156366..f277c6f9ae 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ContentControl.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ContentControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ContentControl}" TargetType="ContentControl">
     <Setter Property="Template">
       <ControlTemplate>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ContextMenu.xaml b/src/Avalonia.Themes.Fluent/Controls/ContextMenu.xaml
index f6900f785f..c8e2873eb6 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ContextMenu.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ContextMenu.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Background="{DynamicResource SystemAccentColor}"
             Margin="16"
diff --git a/src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml b/src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml
index 984a523471..94f1d3cdda 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:sys="using:System"
-                    xmlns:collections="using:System.Collections">
+                    xmlns:collections="using:System.Collections"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
index e71e733eff..58f181bd23 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
@@ -7,7 +7,8 @@
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:sys="using:System">
+        xmlns:sys="using:System"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20" Height="500">
       <StackPanel Spacing="20" VerticalAlignment="Center">
diff --git a/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml b/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
index 9d21e6e758..9384eff8f4 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20" Width="200">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/DropDownButton.xaml b/src/Avalonia.Themes.Fluent/Controls/DropDownButton.xaml
index 421ba0bb18..438ad6cf18 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DropDownButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DropDownButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
     <Design.PreviewWith>
       <Border Padding="20">
         <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/EmbeddableControlRoot.xaml b/src/Avalonia.Themes.Fluent/Controls/EmbeddableControlRoot.xaml
index ee51ef8085..1fc931db36 100644
--- a/src/Avalonia.Themes.Fluent/Controls/EmbeddableControlRoot.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/EmbeddableControlRoot.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type EmbeddableControlRoot}" TargetType="EmbeddableControlRoot">
     <Setter Property="Foreground" Value="{DynamicResource SystemControlForegroundBaseHighBrush}"/>
     <Setter Property="Background" Value="{DynamicResource SystemRegionBrush}"/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/Expander.xaml b/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
index 37e9b71185..adaecc71ab 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
 
   <Design.PreviewWith>
     <Border Padding="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/FluentControls.xaml b/src/Avalonia.Themes.Fluent/Controls/FluentControls.xaml
index 31b0a01b21..deb7d39a89 100644
--- a/src/Avalonia.Themes.Fluent/Controls/FluentControls.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/FluentControls.xaml
@@ -1,6 +1,7 @@
 <Styles
     xmlns="https://github.com/avaloniaui"
-    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    x:ClassModifier="internal">
     <Styles.Resources>
         <ResourceDictionary>
             <ResourceDictionary.MergedDictionaries>
diff --git a/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml b/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
index 2dca5b0770..e8c9ed9b2a 100644
--- a/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Thickness x:Key="FlyoutBorderThemeThickness">1</Thickness>
   <ControlTheme x:Key="{x:Type FlyoutPresenter}" TargetType="FlyoutPresenter">
     <Setter Property="HorizontalContentAlignment" Value="Stretch" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/GridSplitter.xaml b/src/Avalonia.Themes.Fluent/Controls/GridSplitter.xaml
index ca57eccd13..fc08d6b0b6 100644
--- a/src/Avalonia.Themes.Fluent/Controls/GridSplitter.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/GridSplitter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
     <ControlTheme x:Key="{x:Type GridSplitter}" TargetType="GridSplitter">
       <Setter Property="Focusable" Value="True" />
       <Setter Property="MinWidth" Value="6" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/ItemsControl.xaml b/src/Avalonia.Themes.Fluent/Controls/ItemsControl.xaml
index 19a29b9466..91f9536847 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ItemsControl.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ItemsControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ItemsControl}" TargetType="ItemsControl">
     <Setter Property="Template">
       <ControlTemplate>
diff --git a/src/Avalonia.Themes.Fluent/Controls/Label.xaml b/src/Avalonia.Themes.Fluent/Controls/Label.xaml
index ff6909ee87..237da0bfa3 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Label.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Label.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
 
   <ControlTheme x:Key="{x:Type Label}" TargetType="Label">
     <Setter Property="Padding" Value="3"/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
index 05bbbe9558..2dde18a523 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <ListBox>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ListBoxItem.xaml b/src/Avalonia.Themes.Fluent/Controls/ListBoxItem.xaml
index fc1d0c5ff1..4e74406c92 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ListBoxItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ListBoxItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="0">
       <ListBox>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml b/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
index 8519099a27..374daa7ab5 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:dialogs="using:Avalonia.Dialogs"
-        xmlns:internal="using:Avalonia.Dialogs.Internal">
+        xmlns:internal="using:Avalonia.Dialogs.Internal"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20" Width="800" Height="500">
       <dialogs:ManagedFileChooser/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/Menu.xaml b/src/Avalonia.Themes.Fluent/Controls/Menu.xaml
index e6bbbde632..c1640efa8c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Menu.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Menu.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <Menu>
diff --git a/src/Avalonia.Themes.Fluent/Controls/MenuFlyoutPresenter.xaml b/src/Avalonia.Themes.Fluent/Controls/MenuFlyoutPresenter.xaml
index b1f44cc70d..b5dff7b59d 100644
--- a/src/Avalonia.Themes.Fluent/Controls/MenuFlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/MenuFlyoutPresenter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type MenuFlyoutPresenter}" TargetType="MenuFlyoutPresenter">
     <Setter Property="Background" Value="{DynamicResource MenuFlyoutPresenterBackground}" />
     <Setter Property="BorderBrush" Value="{DynamicResource MenuFlyoutPresenterBorderBrush}" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml b/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
index c7ffdd3418..8a2d76b940 100644
--- a/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:conv="using:Avalonia.Controls.Converters">
+                    xmlns:conv="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20" Width="320">
       <StackPanel Spacing="20" HorizontalAlignment="Left">
diff --git a/src/Avalonia.Themes.Fluent/Controls/MenuScrollViewer.xaml b/src/Avalonia.Themes.Fluent/Controls/MenuScrollViewer.xaml
index adca099a10..9dd65b1349 100644
--- a/src/Avalonia.Themes.Fluent/Controls/MenuScrollViewer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/MenuScrollViewer.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
 
   <Design.PreviewWith>
     <ScrollViewer Theme="{DynamicResource FluentMenuScrollViewer}" Width="200" Height="200">
diff --git a/src/Avalonia.Themes.Fluent/Controls/NativeMenuBar.xaml b/src/Avalonia.Themes.Fluent/Controls/NativeMenuBar.xaml
index 515a5a730b..3e28ac3ddd 100644
--- a/src/Avalonia.Themes.Fluent/Controls/NativeMenuBar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/NativeMenuBar.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:local="using:Avalonia.Themes.Fluent">
+                    xmlns:local="using:Avalonia.Themes.Fluent"
+                    x:ClassModifier="internal">
   <local:IBitmapToImageConverter x:Key="AvaloniaThemesFluentNativeMenuBarIBitmapToImageConverter"/>
   <ControlTheme x:Key="{x:Type NativeMenuBar}" TargetType="NativeMenuBar">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml b/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
index 51dcdd42e3..52e7280c95 100644
--- a/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="0" Background="White">
       <NotificationCard Content="Testing" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/NumericUpDown.xaml b/src/Avalonia.Themes.Fluent/Controls/NumericUpDown.xaml
index 872367c6da..1f84ee664c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/NumericUpDown.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/NumericUpDown.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/OverlayPopupHost.xaml b/src/Avalonia.Themes.Fluent/Controls/OverlayPopupHost.xaml
index 28d8fb508c..1316a5bd65 100644
--- a/src/Avalonia.Themes.Fluent/Controls/OverlayPopupHost.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/OverlayPopupHost.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type OverlayPopupHost}" TargetType="OverlayPopupHost">
     <Setter Property="Foreground" Value="{DynamicResource SystemControlForegroundBaseHighBrush}"/>
     <Setter Property="FontSize" Value="{DynamicResource ControlContentThemeFontSize}"/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/PathIcon.xaml b/src/Avalonia.Themes.Fluent/Controls/PathIcon.xaml
index 5584eb3ab9..2a817ccfcb 100644
--- a/src/Avalonia.Themes.Fluent/Controls/PathIcon.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/PathIcon.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <StackPanel>
       <StackPanel.Resources>
diff --git a/src/Avalonia.Themes.Fluent/Controls/PopupRoot.xaml b/src/Avalonia.Themes.Fluent/Controls/PopupRoot.xaml
index 5a924830b1..910c5f8d8c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/PopupRoot.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/PopupRoot.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type PopupRoot}" TargetType="PopupRoot">
     <Setter Property="Background" Value="{x:Null}" />
     <Setter Property="TransparencyLevelHint" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/ProgressBar.xaml b/src/Avalonia.Themes.Fluent/Controls/ProgressBar.xaml
index 64a598e359..adb8551ec3 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ProgressBar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ProgressBar.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Orientation="Horizontal" Spacing="10">
diff --git a/src/Avalonia.Themes.Fluent/Controls/RadioButton.xaml b/src/Avalonia.Themes.Fluent/Controls/RadioButton.xaml
index a1c4ba4f2d..39f89788bb 100644
--- a/src/Avalonia.Themes.Fluent/Controls/RadioButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/RadioButton.xaml
@@ -1,4 +1,5 @@
-<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="10">
diff --git a/src/Avalonia.Themes.Fluent/Controls/RefreshContainer.xaml b/src/Avalonia.Themes.Fluent/Controls/RefreshContainer.xaml
index 8e29e6208f..b030acca30 100644
--- a/src/Avalonia.Themes.Fluent/Controls/RefreshContainer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/RefreshContainer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RefreshContainer}"
                 TargetType="RefreshContainer">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Fluent/Controls/RefreshVisualizer.xaml b/src/Avalonia.Themes.Fluent/Controls/RefreshVisualizer.xaml
index 4e76bee9f5..a9ca8a0a5c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/RefreshVisualizer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/RefreshVisualizer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RefreshVisualizer}"
                 TargetType="RefreshVisualizer">
     <Setter Property="IsTabStop" Value="False"/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/RepeatButton.xaml b/src/Avalonia.Themes.Fluent/Controls/RepeatButton.xaml
index fd04c85fed..b8a06f996a 100644
--- a/src/Avalonia.Themes.Fluent/Controls/RepeatButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/RepeatButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml b/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
index 4544fbe339..531f11a90b 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Orientation="Horizontal" Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml b/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
index 6218fe94ca..886a903a43 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary
   xmlns="https://github.com/avaloniaui"
-  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+  x:ClassModifier="internal">
   <Design.PreviewWith>
     <ScrollViewer Width="200" Height="200"
                   HorizontalScrollBarVisibility="Auto">
diff --git a/src/Avalonia.Themes.Fluent/Controls/SelectableTextBlock.xaml b/src/Avalonia.Themes.Fluent/Controls/SelectableTextBlock.xaml
index 2556f80ef6..b5daa65efc 100644
--- a/src/Avalonia.Themes.Fluent/Controls/SelectableTextBlock.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/SelectableTextBlock.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <SelectableTextBlock Text="Preview" />
   </Design.PreviewWith>
diff --git a/src/Avalonia.Themes.Fluent/Controls/Separator.xaml b/src/Avalonia.Themes.Fluent/Controls/Separator.xaml
index d13bffe5e1..3b4a111a58 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Separator.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Separator.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Separator}" TargetType="Separator">
     <Setter Property="Background" Value="{DynamicResource SystemControlForegroundBaseMediumLowBrush}" />
     <Setter Property="Focusable" Value="False" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/Slider.xaml b/src/Avalonia.Themes.Fluent/Controls/Slider.xaml
index 6e9e37643e..a4102a84d3 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Slider.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Slider.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Margin="20" Width="400" Height="600">
       <DockPanel LastChildFill="True">
diff --git a/src/Avalonia.Themes.Fluent/Controls/SplitButton.xaml b/src/Avalonia.Themes.Fluent/Controls/SplitButton.xaml
index 1a7e72462a..98f8c8238e 100644
--- a/src/Avalonia.Themes.Fluent/Controls/SplitButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/SplitButton.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:converters="using:Avalonia.Controls.Converters">
+        xmlns:converters="using:Avalonia.Controls.Converters"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="60">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/SplitView.xaml b/src/Avalonia.Themes.Fluent/Controls/SplitView.xaml
index 9feb6c7fc6..aaf6ad7dbc 100644
--- a/src/Avalonia.Themes.Fluent/Controls/SplitView.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/SplitView.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:sys="using:System">
+        xmlns:sys="using:System"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Width="400" Height="400">
       <SplitView DisplayMode="Inline"
diff --git a/src/Avalonia.Themes.Fluent/Controls/TabControl.xaml b/src/Avalonia.Themes.Fluent/Controls/TabControl.xaml
index cd89443e1f..13b902a3a8 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TabControl.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TabControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Width="400">
       <TabControl>
diff --git a/src/Avalonia.Themes.Fluent/Controls/TabItem.xaml b/src/Avalonia.Themes.Fluent/Controls/TabItem.xaml
index b11ad4e03a..54eea85743 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TabItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TabItem.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary
     xmlns="https://github.com/avaloniaui"
-    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/TabStrip.xaml b/src/Avalonia.Themes.Fluent/Controls/TabStrip.xaml
index ead6fc41ab..ecaad94482 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TabStrip.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TabStrip.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <TabStrip>
diff --git a/src/Avalonia.Themes.Fluent/Controls/TabStripItem.xaml b/src/Avalonia.Themes.Fluent/Controls/TabStripItem.xaml
index d5440025ae..9c8584f7e5 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TabStripItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TabStripItem.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary
     xmlns="https://github.com/avaloniaui"
-    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/TextBox.xaml b/src/Avalonia.Themes.Fluent/Controls/TextBox.xaml
index 40abac8e86..2c05ad6f64 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TextBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TextBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ThemeVariantScope.xaml b/src/Avalonia.Themes.Fluent/Controls/ThemeVariantScope.xaml
index 21a5506b88..2e8715c9b9 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ThemeVariantScope.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ThemeVariantScope.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ThemeVariantScope}"
                 TargetType="ThemeVariantScope">
     <Setter Property="TextElement.Foreground" Value="{DynamicResource SystemControlForegroundBaseHighBrush}"/>
diff --git a/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
index 39f7b0b224..38868f3cdf 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
@@ -7,7 +7,8 @@
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:sys="using:System">
+        xmlns:sys="using:System"
+        x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20" Height="500">
       <StackPanel Spacing="20" VerticalAlignment="Center">
diff --git a/src/Avalonia.Themes.Fluent/Controls/TitleBar.xaml b/src/Avalonia.Themes.Fluent/Controls/TitleBar.xaml
index 5730b19e78..2eff04218d 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TitleBar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TitleBar.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
     <Design.PreviewWith>
       <Border Height="30" Width="300">
         <TitleBar Background="SkyBlue" Foreground="Black" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/ToggleButton.xaml b/src/Avalonia.Themes.Fluent/Controls/ToggleButton.xaml
index da2021790a..1b54e6deaf 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ToggleButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ToggleButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml b/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
index c88839f7d2..47d7953096 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary
     xmlns="https://github.com/avaloniaui"
-    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    x:ClassModifier="internal">
   <Design.PreviewWith>
     <StackPanel Margin="20" Width="250" Spacing="24">
       <StackPanel Spacing="12" >
diff --git a/src/Avalonia.Themes.Fluent/Controls/ToolTip.xaml b/src/Avalonia.Themes.Fluent/Controls/ToolTip.xaml
index 8b086a8d10..b2fcfc7ddf 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ToolTip.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ToolTip.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/TransitioningContentControl.xaml b/src/Avalonia.Themes.Fluent/Controls/TransitioningContentControl.xaml
index e53fc1aad4..2078322318 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TransitioningContentControl.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TransitioningContentControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TransitioningContentControl}" TargetType="TransitioningContentControl">
     <Setter Property="Template">
       <ControlTemplate>
diff --git a/src/Avalonia.Themes.Fluent/Controls/TreeView.xaml b/src/Avalonia.Themes.Fluent/Controls/TreeView.xaml
index 241d3e2b74..0fdcaf39f8 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TreeView.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TreeView.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Fluent/Controls/TreeViewItem.xaml b/src/Avalonia.Themes.Fluent/Controls/TreeViewItem.xaml
index eff3920b12..c92774bc10 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TreeViewItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TreeViewItem.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:converters="using:Avalonia.Controls.Converters">
+        xmlns:converters="using:Avalonia.Controls.Converters"
+        x:ClassModifier="internal">
 
   <Design.PreviewWith>
     <Border Padding="20"
diff --git a/src/Avalonia.Themes.Fluent/Controls/UserControl.xaml b/src/Avalonia.Themes.Fluent/Controls/UserControl.xaml
index 7dc23f652a..bb75ec8bbc 100644
--- a/src/Avalonia.Themes.Fluent/Controls/UserControl.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/UserControl.xaml
@@ -1,6 +1,7 @@
 <Style xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-       Selector=":is(UserControl)">
+       Selector=":is(UserControl)"
+       x:ClassModifier="internal">
   <Style.Resources>
     <ControlTheme x:Key="FluentUserControl" TargetType="UserControl">
       <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Fluent/Controls/Window.xaml b/src/Avalonia.Themes.Fluent/Controls/Window.xaml
index 8db01fa4c8..52d16e7ada 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Window.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Window.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Window}" TargetType="Window">
     <Setter Property="Background" Value="{DynamicResource SystemRegionBrush}"/>
     <Setter Property="TransparencyBackgroundFallback" Value="{DynamicResource SystemControlBackgroundAltHighBrush}" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/WindowNotificationManager.xaml b/src/Avalonia.Themes.Fluent/Controls/WindowNotificationManager.xaml
index e4cd0b25a6..a62f4adfd6 100644
--- a/src/Avalonia.Themes.Fluent/Controls/WindowNotificationManager.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/WindowNotificationManager.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    x:DataType="WindowNotificationManager">
+                    x:DataType="WindowNotificationManager"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type WindowNotificationManager}" TargetType="WindowNotificationManager">
     <Setter Property="Margin" Value="0 0" />
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Fluent/DensityStyles/Compact.xaml b/src/Avalonia.Themes.Fluent/DensityStyles/Compact.xaml
index b96671b778..d335e6f4b9 100644
--- a/src/Avalonia.Themes.Fluent/DensityStyles/Compact.xaml
+++ b/src/Avalonia.Themes.Fluent/DensityStyles/Compact.xaml
@@ -1,5 +1,6 @@
 <Styles xmlns="https://github.com/avaloniaui" 
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:ClassModifier="internal">
     <Style Selector="TextBlock" >
         <Setter Property="FontSize" Value="14" />
     </Style>
diff --git a/src/Avalonia.Themes.Fluent/FluentTheme.xaml b/src/Avalonia.Themes.Fluent/FluentTheme.xaml
index 0528c40c21..c84772aa61 100644
--- a/src/Avalonia.Themes.Fluent/FluentTheme.xaml
+++ b/src/Avalonia.Themes.Fluent/FluentTheme.xaml
@@ -2,7 +2,7 @@
         xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:fluent="using:Avalonia.Themes.Fluent"
-        xmlns:accents="clr-namespace:Avalonia.Themes.Fluent.Accents">
+        xmlns:accents="using:Avalonia.Themes.Fluent.Accents">
   <Styles.Resources>
     <ResourceDictionary>
       <ResourceDictionary.MergedDictionaries>
diff --git a/src/Avalonia.Themes.Simple/Accents/Base.xaml b/src/Avalonia.Themes.Simple/Accents/Base.xaml
index 0640fe9a4a..ca5c2e7d30 100644
--- a/src/Avalonia.Themes.Simple/Accents/Base.xaml
+++ b/src/Avalonia.Themes.Simple/Accents/Base.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <ResourceDictionary.ThemeDictionaries>
     <ResourceDictionary x:Key="Default">
       <Color x:Key="ThemeBackgroundColor">#FFFFFFFF</Color>
diff --git a/src/Avalonia.Themes.Simple/Avalonia.Themes.Simple.csproj b/src/Avalonia.Themes.Simple/Avalonia.Themes.Simple.csproj
index 03193599ed..39da9a747f 100644
--- a/src/Avalonia.Themes.Simple/Avalonia.Themes.Simple.csproj
+++ b/src/Avalonia.Themes.Simple/Avalonia.Themes.Simple.csproj
@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
-    <!-- NativeMenuBar uses ReflectionBinding -->
-    <NoWarn>$(NoWarn);IL2026</NoWarn>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
diff --git a/src/Avalonia.Themes.Simple/Controls/AdornerLayer.xaml b/src/Avalonia.Themes.Simple/Controls/AdornerLayer.xaml
index 1f3acb07dc..165ab44fc8 100644
--- a/src/Avalonia.Themes.Simple/Controls/AdornerLayer.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/AdornerLayer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type AdornerLayer}" TargetType="AdornerLayer">
     <Setter Property="DefaultFocusAdorner">
       <FocusAdornerTemplate>
diff --git a/src/Avalonia.Themes.Simple/Controls/AutoCompleteBox.xaml b/src/Avalonia.Themes.Simple/Controls/AutoCompleteBox.xaml
index 65dfaf982b..b861c5f3ea 100644
--- a/src/Avalonia.Themes.Simple/Controls/AutoCompleteBox.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/AutoCompleteBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type AutoCompleteBox}"
                 TargetType="AutoCompleteBox">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/Button.xaml b/src/Avalonia.Themes.Simple/Controls/Button.xaml
index 9018677ab6..5599e49ae1 100644
--- a/src/Avalonia.Themes.Simple/Controls/Button.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Button.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Button}"
                 TargetType="Button">
     <Setter Property="Background" Value="{DynamicResource ThemeControlMidBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ButtonSpinner.xaml b/src/Avalonia.Themes.Simple/Controls/ButtonSpinner.xaml
index 57d6eabea4..14472d601f 100644
--- a/src/Avalonia.Themes.Simple/Controls/ButtonSpinner.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ButtonSpinner.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
 
   <ControlTheme x:Key="SimpleButtonSpinnerRepeatButton"
                 BasedOn="{StaticResource {x:Type RepeatButton}}"
diff --git a/src/Avalonia.Themes.Simple/Controls/Calendar.xaml b/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
index 08305319e1..e13f543a90 100644
--- a/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Calendar}"
                 TargetType="Calendar">
     <!--<Setter Property="Focusable" Value="False" />-->
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
index 9e13e1e996..1e06368d24 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type CalendarButton}"
                 TargetType="CalendarButton">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarDatePicker.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarDatePicker.xaml
index a7c7b5f620..60759eebb1 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarDatePicker.xaml
@@ -7,7 +7,8 @@
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type CalendarDatePicker}"
                 TargetType="CalendarDatePicker">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
index 0973a3b752..e16b9f38ba 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type CalendarDayButton}"
                 TargetType="CalendarDayButton">
     <Setter Property="Background" Value="{DynamicResource ThemeAccentBrush2}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
index f022746bf5..e9e9299960 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type CalendarItem}"
                 TargetType="CalendarItem">
     <Setter Property="CornerRadius" Value="1" />
diff --git a/src/Avalonia.Themes.Simple/Controls/CaptionButtons.xaml b/src/Avalonia.Themes.Simple/Controls/CaptionButtons.xaml
index 8f68d9809f..e5978919fa 100644
--- a/src/Avalonia.Themes.Simple/Controls/CaptionButtons.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CaptionButtons.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="20">
diff --git a/src/Avalonia.Themes.Simple/Controls/Carousel.xaml b/src/Avalonia.Themes.Simple/Controls/Carousel.xaml
index 91e331693e..b94ef9b5d9 100644
--- a/src/Avalonia.Themes.Simple/Controls/Carousel.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Carousel.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Carousel}" TargetType="Carousel">
     <Setter Property="Template">
       <ControlTemplate>
diff --git a/src/Avalonia.Themes.Simple/Controls/CheckBox.xaml b/src/Avalonia.Themes.Simple/Controls/CheckBox.xaml
index 10e0b883d5..68e969c140 100644
--- a/src/Avalonia.Themes.Simple/Controls/CheckBox.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CheckBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type CheckBox}"
                 TargetType="CheckBox">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ComboBox.xaml b/src/Avalonia.Themes.Simple/Controls/ComboBox.xaml
index 8b751187d6..a54857abc9 100644
--- a/src/Avalonia.Themes.Simple/Controls/ComboBox.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ComboBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ComboBox}"
                 TargetType="ComboBox">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ComboBoxItem.xaml b/src/Avalonia.Themes.Simple/Controls/ComboBoxItem.xaml
index c3d8b6f900..da1b964871 100644
--- a/src/Avalonia.Themes.Simple/Controls/ComboBoxItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ComboBoxItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ComboBoxItem}"
                 TargetType="ComboBoxItem">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ContentControl.xaml b/src/Avalonia.Themes.Simple/Controls/ContentControl.xaml
index 415b1dc721..571a276a49 100644
--- a/src/Avalonia.Themes.Simple/Controls/ContentControl.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ContentControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ContentControl}"
                 TargetType="ContentControl">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Simple/Controls/ContextMenu.xaml b/src/Avalonia.Themes.Simple/Controls/ContextMenu.xaml
index 3317178979..215f4eec5a 100644
--- a/src/Avalonia.Themes.Simple/Controls/ContextMenu.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ContextMenu.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ContextMenu}"
                 TargetType="ContextMenu">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/DataValidationErrors.xaml b/src/Avalonia.Themes.Simple/Controls/DataValidationErrors.xaml
index a4e5ab2d90..ec5ad87bbc 100644
--- a/src/Avalonia.Themes.Simple/Controls/DataValidationErrors.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DataValidationErrors.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type DataValidationErrors}"
                 TargetType="DataValidationErrors">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml b/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
index 6cf352518a..6ead5019c6 100644
--- a/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
@@ -7,7 +7,8 @@
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Height="500"
             Padding="20">
diff --git a/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml b/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
index 5f1dea692f..5ba4e058ed 100644
--- a/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
@@ -6,7 +6,8 @@
 -->
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Width="200"
             Padding="20">
diff --git a/src/Avalonia.Themes.Simple/Controls/DropDownButton.xaml b/src/Avalonia.Themes.Simple/Controls/DropDownButton.xaml
index 6a50cd6e36..6d79d420f3 100644
--- a/src/Avalonia.Themes.Simple/Controls/DropDownButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DropDownButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type DropDownButton}"
                 TargetType="DropDownButton">
     <Setter Property="Background" Value="{DynamicResource ThemeControlMidBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/EmbeddableControlRoot.xaml b/src/Avalonia.Themes.Simple/Controls/EmbeddableControlRoot.xaml
index 3ea1515cc3..87c940c281 100644
--- a/src/Avalonia.Themes.Simple/Controls/EmbeddableControlRoot.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/EmbeddableControlRoot.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type EmbeddableControlRoot}"
                 TargetType="EmbeddableControlRoot">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/Expander.xaml b/src/Avalonia.Themes.Simple/Controls/Expander.xaml
index 9920c9445a..cdc2894979 100644
--- a/src/Avalonia.Themes.Simple/Controls/Expander.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Expander.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Width="350"
diff --git a/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml b/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
index 08959cfbbe..b6cf899fd5 100644
--- a/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type FlyoutPresenter}"
                 TargetType="FlyoutPresenter">
     <Setter Property="HorizontalContentAlignment" Value="Stretch" />
diff --git a/src/Avalonia.Themes.Simple/Controls/GridSplitter.xaml b/src/Avalonia.Themes.Simple/Controls/GridSplitter.xaml
index f2a3f01397..c4385ab0b4 100644
--- a/src/Avalonia.Themes.Simple/Controls/GridSplitter.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/GridSplitter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type GridSplitter}"
                 TargetType="GridSplitter">
     <Setter Property="Focusable" Value="True" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ItemsControl.xaml b/src/Avalonia.Themes.Simple/Controls/ItemsControl.xaml
index 8cf4e0be08..ba6b37fd90 100644
--- a/src/Avalonia.Themes.Simple/Controls/ItemsControl.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ItemsControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ItemsControl}"
                 TargetType="ItemsControl">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Simple/Controls/Label.xaml b/src/Avalonia.Themes.Simple/Controls/Label.xaml
index 0faa4852f2..2c9bb15742 100644
--- a/src/Avalonia.Themes.Simple/Controls/Label.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Label.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Label}"
                 TargetType="Label">
     <Setter Property="Padding" Value="3" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ListBox.xaml b/src/Avalonia.Themes.Simple/Controls/ListBox.xaml
index a51fcbf72e..eeefa498a7 100644
--- a/src/Avalonia.Themes.Simple/Controls/ListBox.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ListBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ListBox}"
                 TargetType="ListBox">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ListBoxItem.xaml b/src/Avalonia.Themes.Simple/Controls/ListBoxItem.xaml
index 4d918326c8..c2a96c71a6 100644
--- a/src/Avalonia.Themes.Simple/Controls/ListBoxItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ListBoxItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ListBoxItem}"
                 TargetType="ListBoxItem">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml b/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
index cc049938ad..24e5247139 100644
--- a/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:dialogs="using:Avalonia.Dialogs"
-                    xmlns:internal="using:Avalonia.Dialogs.Internal">
+                    xmlns:internal="using:Avalonia.Dialogs.Internal"
+                    x:ClassModifier="internal">
   <DrawingGroup x:Key="LevelUp">
     <GeometryDrawing Brush="#00FFFFFF" Geometry="F1M16,16L0,16 0,0 16,0z" />
     <GeometryDrawing Brush="#FFF6F6F6"
diff --git a/src/Avalonia.Themes.Simple/Controls/Menu.xaml b/src/Avalonia.Themes.Simple/Controls/Menu.xaml
index c64527d63c..1024cae7a4 100644
--- a/src/Avalonia.Themes.Simple/Controls/Menu.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Menu.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
 
   <ControlTheme x:Key="SimpleTopLevelMenuItem"
                 TargetType="MenuItem">
diff --git a/src/Avalonia.Themes.Simple/Controls/MenuFlyoutPresenter.xaml b/src/Avalonia.Themes.Simple/Controls/MenuFlyoutPresenter.xaml
index 05337d774f..73835b8155 100644
--- a/src/Avalonia.Themes.Simple/Controls/MenuFlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/MenuFlyoutPresenter.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type MenuFlyoutPresenter}"
                 TargetType="MenuFlyoutPresenter">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml b/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
index 59ddcdf325..063c0d3d68 100644
--- a/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
@@ -1,7 +1,8 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:conv="using:Avalonia.Controls.Converters"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <conv:PlatformKeyGestureConverter x:Key="KeyGestureConverter" />
 
   <ControlTheme x:Key="{x:Type MenuItem}"
diff --git a/src/Avalonia.Themes.Simple/Controls/NativeMenuBar.xaml b/src/Avalonia.Themes.Simple/Controls/NativeMenuBar.xaml
index 625bf71e66..9139f96a2a 100644
--- a/src/Avalonia.Themes.Simple/Controls/NativeMenuBar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/NativeMenuBar.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:default="using:Avalonia.Themes.Simple">
+                    xmlns:default="using:Avalonia.Themes.Simple"
+                    x:ClassModifier="internal">
   <default:IBitmapToImageConverter x:Key="AvaloniaThemesSimpleNativeMenuBarIBitmapToImageConverter" />
   <ControlTheme x:Key="{x:Type NativeMenuBar}"
                 TargetType="NativeMenuBar">
diff --git a/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml b/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
index 524f964afc..62e73a8dd0 100644
--- a/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type NotificationCard}"
                 TargetType="NotificationCard">
     <Setter Property="Background" Value="{DynamicResource NotificationCardBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/NumericUpDown.xaml b/src/Avalonia.Themes.Simple/Controls/NumericUpDown.xaml
index d3adfb31e0..4ce6a20dc6 100644
--- a/src/Avalonia.Themes.Simple/Controls/NumericUpDown.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/NumericUpDown.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type NumericUpDown}"
                 TargetType="NumericUpDown">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/OverlayPopupHost.xaml b/src/Avalonia.Themes.Simple/Controls/OverlayPopupHost.xaml
index 4c7864473b..c70721aac7 100644
--- a/src/Avalonia.Themes.Simple/Controls/OverlayPopupHost.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/OverlayPopupHost.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type OverlayPopupHost}"
                 TargetType="OverlayPopupHost">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/PathIcon.xaml b/src/Avalonia.Themes.Simple/Controls/PathIcon.xaml
index 4116b5784e..9e39ba4645 100644
--- a/src/Avalonia.Themes.Simple/Controls/PathIcon.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/PathIcon.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type PathIcon}"
                 TargetType="PathIcon">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundColor}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/PopupRoot.xaml b/src/Avalonia.Themes.Simple/Controls/PopupRoot.xaml
index 33c8d0764e..aaf51a2cef 100644
--- a/src/Avalonia.Themes.Simple/Controls/PopupRoot.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/PopupRoot.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type PopupRoot}"
                 TargetType="PopupRoot">
     <Setter Property="Background" Value="{x:Null}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ProgressBar.xaml b/src/Avalonia.Themes.Simple/Controls/ProgressBar.xaml
index 1f4bf006a0..4278c7ee28 100644
--- a/src/Avalonia.Themes.Simple/Controls/ProgressBar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ProgressBar.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Padding="20">
       <StackPanel Spacing="10">
diff --git a/src/Avalonia.Themes.Simple/Controls/RadioButton.xaml b/src/Avalonia.Themes.Simple/Controls/RadioButton.xaml
index c837b44402..ea138d8806 100644
--- a/src/Avalonia.Themes.Simple/Controls/RadioButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/RadioButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RadioButton}"
                 TargetType="RadioButton">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/RefreshContainer.xaml b/src/Avalonia.Themes.Simple/Controls/RefreshContainer.xaml
index 04b2a1bf29..0a293cc977 100644
--- a/src/Avalonia.Themes.Simple/Controls/RefreshContainer.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/RefreshContainer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RefreshContainer}"
                 TargetType="RefreshContainer">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Simple/Controls/RefreshVisualizer.xaml b/src/Avalonia.Themes.Simple/Controls/RefreshVisualizer.xaml
index bd7e43530a..09f15e4b2a 100644
--- a/src/Avalonia.Themes.Simple/Controls/RefreshVisualizer.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/RefreshVisualizer.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RefreshVisualizer}"
                 TargetType="RefreshVisualizer">
     <Setter Property="IsTabStop"
diff --git a/src/Avalonia.Themes.Simple/Controls/RepeatButton.xaml b/src/Avalonia.Themes.Simple/Controls/RepeatButton.xaml
index 73cfd4d810..9da320a79d 100644
--- a/src/Avalonia.Themes.Simple/Controls/RepeatButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/RepeatButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type RepeatButton}"
                 TargetType="RepeatButton">
     <Setter Property="Background" Value="{DynamicResource ThemeControlMidBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ScrollBar.xaml b/src/Avalonia.Themes.Simple/Controls/ScrollBar.xaml
index d28ba66f6d..8b647c8299 100644
--- a/src/Avalonia.Themes.Simple/Controls/ScrollBar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ScrollBar.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ScrollBar}"
                 TargetType="ScrollBar">
     <Setter Property="Cursor" Value="Arrow" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ScrollViewer.xaml b/src/Avalonia.Themes.Simple/Controls/ScrollViewer.xaml
index 4f6fc5f322..2b36b118c3 100644
--- a/src/Avalonia.Themes.Simple/Controls/ScrollViewer.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ScrollViewer.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ScrollViewer}"
                 TargetType="ScrollViewer">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/SelectableTextBlock.xaml b/src/Avalonia.Themes.Simple/Controls/SelectableTextBlock.xaml
index e504a8cf8e..504e727fa0 100644
--- a/src/Avalonia.Themes.Simple/Controls/SelectableTextBlock.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/SelectableTextBlock.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <SelectableTextBlock Text="Preview" />
   </Design.PreviewWith>
diff --git a/src/Avalonia.Themes.Simple/Controls/Separator.xaml b/src/Avalonia.Themes.Simple/Controls/Separator.xaml
index e142cf29ad..0d7202c8b4 100644
--- a/src/Avalonia.Themes.Simple/Controls/Separator.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Separator.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Separator}"
                 TargetType="Separator">
     <Setter Property="Focusable" Value="False" />
diff --git a/src/Avalonia.Themes.Simple/Controls/SimpleControls.xaml b/src/Avalonia.Themes.Simple/Controls/SimpleControls.xaml
index dc533488c9..3b4a1d8104 100644
--- a/src/Avalonia.Themes.Simple/Controls/SimpleControls.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/SimpleControls.xaml
@@ -1,5 +1,6 @@
 <Styles xmlns="https://github.com/avaloniaui"
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:ClassModifier="internal">
   <Styles.Resources>
     <ResourceDictionary>
       <ResourceDictionary.MergedDictionaries>
diff --git a/src/Avalonia.Themes.Simple/Controls/Slider.xaml b/src/Avalonia.Themes.Simple/Controls/Slider.xaml
index 851ee1b78a..da840dbbd5 100644
--- a/src/Avalonia.Themes.Simple/Controls/Slider.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Slider.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="SliderRepeatTrackTheme"
                 TargetType="RepeatButton">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/SplitButton.xaml b/src/Avalonia.Themes.Simple/Controls/SplitButton.xaml
index 2a7dc081f0..7562c9151e 100644
--- a/src/Avalonia.Themes.Simple/Controls/SplitButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/SplitButton.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
 
   <!-- This style is based on the Fluent v1 style. -->
 
diff --git a/src/Avalonia.Themes.Simple/Controls/SplitView.xaml b/src/Avalonia.Themes.Simple/Controls/SplitView.xaml
index f839e9a598..8d4851add8 100644
--- a/src/Avalonia.Themes.Simple/Controls/SplitView.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/SplitView.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Width="400" Height="400">
       <SplitView DisplayMode="Inline"
diff --git a/src/Avalonia.Themes.Simple/Controls/TabControl.xaml b/src/Avalonia.Themes.Simple/Controls/TabControl.xaml
index c3cecb4fb8..beb6782098 100644
--- a/src/Avalonia.Themes.Simple/Controls/TabControl.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TabControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TabControl}"
                 TargetType="TabControl">
     <Setter Property="Padding" Value="8" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TabItem.xaml b/src/Avalonia.Themes.Simple/Controls/TabItem.xaml
index 7b6a1d1116..50a269bf79 100644
--- a/src/Avalonia.Themes.Simple/Controls/TabItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TabItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TabItem}"
                 TargetType="TabItem">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TabStrip.xaml b/src/Avalonia.Themes.Simple/Controls/TabStrip.xaml
index fd12eaa258..9d08c73453 100644
--- a/src/Avalonia.Themes.Simple/Controls/TabStrip.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TabStrip.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TabStrip}"
                 TargetType="TabStrip">
     <Setter Property="Template">
diff --git a/src/Avalonia.Themes.Simple/Controls/TabStripItem.xaml b/src/Avalonia.Themes.Simple/Controls/TabStripItem.xaml
index b4d7218ec3..f0609bf66b 100644
--- a/src/Avalonia.Themes.Simple/Controls/TabStripItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TabStripItem.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TabStripItem}"
                 TargetType="TabStripItem">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TextBox.xaml b/src/Avalonia.Themes.Simple/Controls/TextBox.xaml
index b835bf10aa..63da3cee44 100644
--- a/src/Avalonia.Themes.Simple/Controls/TextBox.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TextBox.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <StreamGeometry x:Key="TextBoxClearButtonData">M 11.416016,10 20,1.4160156 18.583984,0 10,8.5839846 1.4160156,0 0,1.4160156 8.5839844,10 0,18.583985 1.4160156,20 10,11.416015 18.583984,20 20,18.583985 Z</StreamGeometry>
   <StreamGeometry x:Key="PasswordBoxRevealButtonData">m10.051 7.0032c2.215 0 4.0105 1.7901 4.0105 3.9984s-1.7956 3.9984-4.0105 3.9984c-2.215 0-4.0105-1.7901-4.0105-3.9984s1.7956-3.9984 4.0105-3.9984zm0 1.4994c-1.3844 0-2.5066 1.1188-2.5066 2.499s1.1222 2.499 2.5066 2.499 2.5066-1.1188 2.5066-2.499-1.1222-2.499-2.5066-2.499zm0-5.0026c4.6257 0 8.6188 3.1487 9.7267 7.5613 0.10085 0.40165-0.14399 0.80877-0.54686 0.90931-0.40288 0.10054-0.81122-0.14355-0.91208-0.54521-0.94136-3.7492-4.3361-6.4261-8.2678-6.4261-3.9334 0-7.3292 2.6792-8.2689 6.4306-0.10063 0.40171-0.50884 0.64603-0.91177 0.54571s-0.648-0.5073-0.54737-0.90901c1.106-4.4152 5.1003-7.5667 9.728-7.5667z</StreamGeometry>
   <StreamGeometry x:Key="PasswordBoxHideButtonData">m0.21967 0.21965c-0.26627 0.26627-0.29047 0.68293-0.07262 0.97654l0.07262 0.08412 4.0346 4.0346c-1.922 1.3495-3.3585 3.365-3.9554 5.7495-0.10058 0.4018 0.14362 0.8091 0.54543 0.9097 0.40182 0.1005 0.80909-0.1436 0.90968-0.5455 0.52947-2.1151 1.8371-3.8891 3.5802-5.0341l1.8096 1.8098c-0.70751 0.7215-1.1438 1.71-1.1438 2.8003 0 2.2092 1.7909 4 4 4 1.0904 0 2.0788-0.4363 2.8004-1.1438l5.9193 5.9195c0.2929 0.2929 0.7677 0.2929 1.0606 0 0.2663-0.2662 0.2905-0.6829 0.0726-0.9765l-0.0726-0.0841-6.1135-6.1142 0.0012-0.0015-1.2001-1.1979-2.8699-2.8693 2e-3 -8e-4 -2.8812-2.8782 0.0012-0.0018-1.1333-1.1305-4.3064-4.3058c-0.29289-0.29289-0.76777-0.29289-1.0607 0zm7.9844 9.0458 3.5351 3.5351c-0.45 0.4358-1.0633 0.704-1.7392 0.704-1.3807 0-2.5-1.1193-2.5-2.5 0-0.6759 0.26824-1.2892 0.7041-1.7391zm1.7959-5.7655c-1.0003 0-1.9709 0.14807-2.8889 0.425l1.237 1.2362c0.5358-0.10587 1.0883-0.16119 1.6519-0.16119 3.9231 0 7.3099 2.6803 8.2471 6.4332 0.1004 0.4018 0.5075 0.6462 0.9094 0.5459 0.4019-0.1004 0.6463-0.5075 0.5459-0.9094-1.103-4.417-5.0869-7.5697-9.7024-7.5697zm0.1947 3.5093 3.8013 3.8007c-0.1018-2.0569-1.7488-3.7024-3.8013-3.8007z</StreamGeometry>
diff --git a/src/Avalonia.Themes.Simple/Controls/ThemeVariantScope.xaml b/src/Avalonia.Themes.Simple/Controls/ThemeVariantScope.xaml
index a6022fb263..2eb157cf6b 100644
--- a/src/Avalonia.Themes.Simple/Controls/ThemeVariantScope.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ThemeVariantScope.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ThemeVariantScope}"
                 TargetType="ThemeVariantScope">
     <Setter Property="TextElement.Foreground" Value="{DynamicResource ThemeForegroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml b/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
index 5acbc41a68..adac54a262 100644
--- a/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
@@ -7,7 +7,8 @@
 
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:sys="using:System">
+                    xmlns:sys="using:System"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border Height="500"
             Padding="20">
diff --git a/src/Avalonia.Themes.Simple/Controls/TitleBar.xaml b/src/Avalonia.Themes.Simple/Controls/TitleBar.xaml
index a06dfbb834..67b1eae9da 100644
--- a/src/Avalonia.Themes.Simple/Controls/TitleBar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TitleBar.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <Border>
       <TitleBar Width="300"
diff --git a/src/Avalonia.Themes.Simple/Controls/ToggleButton.xaml b/src/Avalonia.Themes.Simple/Controls/ToggleButton.xaml
index 2cfbcf6b7a..ad05f15f84 100644
--- a/src/Avalonia.Themes.Simple/Controls/ToggleButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ToggleButton.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ToggleButton}"
                 TargetType="ToggleButton">
     <Setter Property="Background" Value="{DynamicResource ThemeControlMidBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml b/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
index f7223c46c0..a51aeb9ee6 100644
--- a/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <Design.PreviewWith>
     <StackPanel Margin="20" Width="250" Spacing="24">
       <StackPanel Spacing="12">
diff --git a/src/Avalonia.Themes.Simple/Controls/ToolTip.xaml b/src/Avalonia.Themes.Simple/Controls/ToolTip.xaml
index c4fddd8c4c..2c67e2c650 100644
--- a/src/Avalonia.Themes.Simple/Controls/ToolTip.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ToolTip.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type ToolTip}"
                 TargetType="ToolTip">
     <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TransitioningContentControl.xaml b/src/Avalonia.Themes.Simple/Controls/TransitioningContentControl.xaml
index fa8d749b1f..ceccdf56c7 100644
--- a/src/Avalonia.Themes.Simple/Controls/TransitioningContentControl.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TransitioningContentControl.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TransitioningContentControl}"
                 TargetType="TransitioningContentControl">
     <!--  Set Defaults  -->
diff --git a/src/Avalonia.Themes.Simple/Controls/TreeView.xaml b/src/Avalonia.Themes.Simple/Controls/TreeView.xaml
index f2f451fe6f..d76bf6c393 100644
--- a/src/Avalonia.Themes.Simple/Controls/TreeView.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TreeView.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type TreeView}"
                 TargetType="TreeView">
     <Setter Property="Background" Value="Transparent" />
diff --git a/src/Avalonia.Themes.Simple/Controls/TreeViewItem.xaml b/src/Avalonia.Themes.Simple/Controls/TreeViewItem.xaml
index 8e85bcbd44..c3c3801ec0 100644
--- a/src/Avalonia.Themes.Simple/Controls/TreeViewItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TreeViewItem.xaml
@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                    xmlns:converters="using:Avalonia.Controls.Converters">
+                    xmlns:converters="using:Avalonia.Controls.Converters"
+                    x:ClassModifier="internal">
   <converters:MarginMultiplierConverter x:Key="LeftMarginConverter"
                                         Indent="16"
                                         Left="True" />
diff --git a/src/Avalonia.Themes.Simple/Controls/UserControl.xaml b/src/Avalonia.Themes.Simple/Controls/UserControl.xaml
index 3316b0298c..7f33b803d7 100644
--- a/src/Avalonia.Themes.Simple/Controls/UserControl.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/UserControl.xaml
@@ -1,6 +1,7 @@
 <Style xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-       Selector=":is(UserControl)">
+       Selector=":is(UserControl)"
+       x:ClassModifier="internal">
   <Style.Resources>
     <ControlTheme x:Key="SimpleUserControl"
                   TargetType="UserControl">
diff --git a/src/Avalonia.Themes.Simple/Controls/Window.xaml b/src/Avalonia.Themes.Simple/Controls/Window.xaml
index 0a0363c2d0..1a1c9f40cd 100644
--- a/src/Avalonia.Themes.Simple/Controls/Window.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Window.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type Window}"
                 TargetType="Window">
     <Setter Property="FontFamily" Value="{DynamicResource ContentControlThemeFontFamily}" />
diff --git a/src/Avalonia.Themes.Simple/Controls/WindowNotificationManager.xaml b/src/Avalonia.Themes.Simple/Controls/WindowNotificationManager.xaml
index 6dacf63be5..ede24fd6eb 100644
--- a/src/Avalonia.Themes.Simple/Controls/WindowNotificationManager.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/WindowNotificationManager.xaml
@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    x:ClassModifier="internal">
   <ControlTheme x:Key="{x:Type WindowNotificationManager}"
                 TargetType="WindowNotificationManager">
     <Setter Property="Margin" Value="0 0 8 8" />
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
index e3d154ffdd..e2aab7d685 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
@@ -231,8 +231,8 @@ namespace Avalonia.Markup.Xaml.XamlIl
                                ?? ((IXamlAstValueNode)parsed.Root).Type.GetClrType().Name;
                 var tb = _sreBuilder.DefineType("Builder_" + Guid.NewGuid().ToString("N") + "_" + xamlName);
                 var builder = _sreTypeSystem.CreateTypeBuilder(tb);
-                parsedDocuments.Add(new XamlDocumentResource(parsed, document.BaseUri?.ToString(), null, null,
-                    builder,
+                parsedDocuments.Add(new XamlDocumentResource(parsed, document.BaseUri?.ToString(),
+                    null, null, true, builder,
                     compiler.DefinePopulateMethod(builder, parsed, AvaloniaXamlIlCompiler.PopulateName, true),
                     document.RootInstance is null ? compiler.DefineBuildMethod(builder, parsed, AvaloniaXamlIlCompiler.BuildName, true) : null));
                 originalDocuments.Add(document);
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/GroupTransformers/XamlIncludeGroupTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/GroupTransformers/XamlIncludeGroupTransformer.cs
index b6a4b599fa..28a48e5855 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/GroupTransformers/XamlIncludeGroupTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/GroupTransformers/XamlIncludeGroupTransformer.cs
@@ -108,7 +108,7 @@ internal class AvaloniaXamlIncludeTransformer : IXamlAstGroupTransformer
         }
 
         var relativeName = "Build:" + assetPath.Substring(assemblyNameSeparator);
-        var buildMethod = avaResType.FindMethod(m => m.Name == relativeName);
+        var buildMethod = avaResType.FindMethod(m => m.Name == relativeName && m.IsPublic);
         if (buildMethod is not null)
         {
             return FromMethod(context, buildMethod, sourceUriNode, expectedLoadedType, node, assetPathUri, assembly, additionalProperties);
@@ -119,7 +119,7 @@ internal class AvaloniaXamlIncludeTransformer : IXamlAstGroupTransformer
         }
 
         return context.ParseError(
-            $"Unable to resolve XAML resource \"{assetPathUri}\" in the \"{assembly}\" assembly.",
+            $"Unable to resolve XAML resource \"{assetPathUri}\" in the \"{assembly}\" assembly. Make sure this file exists and is public.",
             sourceUriNode, node);
     }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlDocumentResource.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlDocumentResource.cs
index d5d452a9f3..932fe067af 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlDocumentResource.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlDocumentResource.cs
@@ -13,6 +13,7 @@ internal class XamlDocumentResource : IXamlDocumentResource
         string? uri,
         IFileSource? fileSource,
         IXamlType? classType,
+        bool isPublic,
         IXamlTypeBuilder<IXamlILEmitter> typeBuilder,
         IXamlMethodBuilder<IXamlILEmitter> populateMethod,
         IXamlMethodBuilder<IXamlILEmitter>? buildMethod)
@@ -21,6 +22,7 @@ internal class XamlDocumentResource : IXamlDocumentResource
         Uri = uri;
         FileSource = fileSource;
         ClassType = classType;
+        IsPublic = isPublic;
         TypeBuilder = typeBuilder;
         PopulateMethod = populateMethod;
         BuildMethod = buildMethod;
@@ -31,6 +33,7 @@ internal class XamlDocumentResource : IXamlDocumentResource
     public IFileSource? FileSource { get; }
 
     public IXamlType? ClassType { get; }
+    public bool IsPublic { get; }
     public IXamlTypeBuilder<IXamlILEmitter> TypeBuilder { get; }
     public IXamlMethodBuilder<IXamlILEmitter> PopulateMethod { get; }
     public IXamlMethodBuilder<IXamlILEmitter>? BuildMethod { get; }