From 13f272d92816783a8c71df1bdb47889da756e05f Mon Sep 17 00:00:00 2001
From: Julien Lebosquain <julien@lebosquain.net>
Date: Mon, 17 Aug 2026 07:30:35 +0000
Subject: [PATCH] Implement WindowDrawnDecorations.TitleBarDecorations (#21969)

* Implement WindowDrawnDecorations.TitleBarDecorations

* Add TitleBarDecorations sample to ControlCatalog
---
 samples/ControlCatalog/MainWindow.xaml        |  1 +
 .../Pages/WindowCustomizationsPage.xaml       | 59 +++++++++---
 samples/ControlCatalog/ScrollPage.xaml        |  2 +-
 .../ViewModels/MainWindowViewModel.cs         | 52 +++++++++++
 .../Chrome/TitleBarDecorations.cs             | 45 +++++++++
 .../Chrome/WindowDrawnDecorations.cs          | 59 ++++++++++--
 .../Controls/WindowDrawnDecorations.xaml      | 18 +++-
 .../Controls/WindowDrawnDecorations.xaml      | 18 +++-
 .../WindowTests.cs                            | 92 +++++++++++++++++++
 9 files changed, 320 insertions(+), 26 deletions(-)
 create mode 100644 src/Avalonia.Controls/Chrome/TitleBarDecorations.cs

diff --git a/samples/ControlCatalog/MainWindow.xaml b/samples/ControlCatalog/MainWindow.xaml
index d839689db7..308b29c572 100644
--- a/samples/ControlCatalog/MainWindow.xaml
+++ b/samples/ControlCatalog/MainWindow.xaml
@@ -12,6 +12,7 @@
         CanResize="{Binding CanResize}"
         CanMinimize="{Binding CanMinimize}"
         CanMaximize="{Binding CanMaximize}"
+        WindowDrawnDecorations.TitleBarDecorations="{Binding TitleBarDecorations}"
         Win32Properties.WindowCornerPreference="{Binding Win32WindowCornerPreference}"
         x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}"
         x:DataType="vm:MainWindowViewModel">
diff --git a/samples/ControlCatalog/Pages/WindowCustomizationsPage.xaml b/samples/ControlCatalog/Pages/WindowCustomizationsPage.xaml
index 5114dd16e9..f304f78898 100644
--- a/samples/ControlCatalog/Pages/WindowCustomizationsPage.xaml
+++ b/samples/ControlCatalog/Pages/WindowCustomizationsPage.xaml
@@ -9,28 +9,58 @@
              x:DataType="viewModels:MainWindowViewModel"
              x:CompileBindings="True"
              DataContext="{Binding $parent[Window].DataContext}">
-  <StackPanel>
+  <StackPanel Spacing="20">
 
     <StackPanel
-      Spacing="10"
-      Margin="25"
       IsEnabled="{OnFormFactor false, Desktop=true}">
 
-      <TextBlock Classes="h2"
+      <TextBlock Classes="h1"
                  Text="Desktop properties"
                  Margin="4" />
 
       <CheckBox Content="Extend Client Area to Decorations"
                 IsChecked="{Binding ExtendClientAreaEnabled}" />
 
-      <DockPanel IsEnabled="{Binding ExtendClientAreaEnabled}">
+      <StackPanel IsVisible="{Binding ExtendClientAreaEnabled}"
+                  Margin="28,0,0,0">
 
-        <Slider Minimum="-1"
-                Maximum="200"
-                Value="{Binding TitleBarHeight}"
-                Margin="8,-10" />
+        <Grid ColumnDefinitions="Auto,*,Auto">
 
-      </DockPanel>
+          <TextBlock Text="Height:"
+                     VerticalAlignment="Center"
+                     Grid.Column="0" />
+
+          <Slider Minimum="-1"
+                  Maximum="200"
+                  Value="{Binding TitleBarHeight}"
+                  TickFrequency="1"
+                  IsSnapToTickEnabled="True"
+                  Margin="8,-10"
+                  Grid.Column="1" />
+
+          <TextBlock Text="{Binding TitleBarHeight, StringFormat=F0}"
+                     MinWidth="50"
+                     VerticalAlignment="Center"
+                     Grid.Column="2" />
+
+        </Grid>
+
+        <CheckBox Content="Title"
+                  IsChecked="{Binding ShowTitle}" />
+
+        <CheckBox Content="Full Screen Button"
+                  IsChecked="{Binding ShowFullScreenButton}" />
+
+        <CheckBox Content="Minimize Button"
+                  IsChecked="{Binding ShowMinimizeButton}" />
+
+        <CheckBox Content="Maximize Button"
+                  IsChecked="{Binding ShowMaximizeButton}" />
+
+        <CheckBox Content="Close Button"
+                  IsChecked="{Binding ShowCloseButton}" />
+
+      </StackPanel>
 
       <CheckBox Content="Can Resize"
                 IsChecked="{Binding CanResize}" />
@@ -45,7 +75,7 @@
       <DockPanel>
 
         <Label Content="Corner Preference (Windows 11+): "
-               Margin="4"
+               Margin="0,4"
                DockPanel.Dock="Left" />
 
         <ComboBox ItemsSource="{Binding Win32WindowCornerPreferences}"
@@ -57,11 +87,12 @@
 
     </StackPanel>
 
-    <StackPanel Spacing="10" Margin="25" IsEnabled="{OnFormFactor false, Mobile=true}">
-      <TextBlock Classes="h2" Text="Mobile properties" Margin="4" />
+    <StackPanel IsEnabled="{OnFormFactor false, Mobile=true}">
+      <TextBlock Classes="h1" Text="Mobile properties" Margin="4" />
       <CheckBox Content="Is System Bar Visible" IsChecked="{Binding IsSystemBarVisible}" />
       <CheckBox Content="Display Edge To Edge" IsChecked="{Binding DisplayEdgeToEdge}" />
-      <TextBlock Text="{Binding SafeAreaPadding, StringFormat='Safe Area Padding: {0}'}" />
+      <TextBlock Text="{Binding SafeAreaPadding, StringFormat='Safe Area Padding: {0}'}"
+                 Margin="0,4" />
     </StackPanel>
 
   </StackPanel>
diff --git a/samples/ControlCatalog/ScrollPage.xaml b/samples/ControlCatalog/ScrollPage.xaml
index 6d5ecb815e..8c6157018f 100644
--- a/samples/ControlCatalog/ScrollPage.xaml
+++ b/samples/ControlCatalog/ScrollPage.xaml
@@ -15,7 +15,7 @@
                             HorizontalContentAlignment="Stretch"
                             IsVisible="False" />
 
-          <ScrollViewer Margin="20,20,5,0"
+          <ScrollViewer Padding="20"
             HorizontalScrollBarVisibility="Disabled">
             <ContentPresenter Name="PART_ContentPresenter"
                             HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
diff --git a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
index 5d14cca1ee..445261950e 100644
--- a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
+++ b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
@@ -1,8 +1,10 @@
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Controls.Chrome;
 using Avalonia.Dialogs;
 using System;
 using System.ComponentModel.DataAnnotations;
+using System.Runtime.CompilerServices;
 using Avalonia;
 using MiniMvvm;
 
@@ -122,6 +124,56 @@ namespace ControlCatalog.ViewModels
             set { RaiseAndSetIfChanged(ref _selectedDecorationIndex, value); }
         }
 
+        public TitleBarDecorations TitleBarDecorations
+        {
+            get;
+            set { RaiseAndSetIfChanged(ref field, value); }
+        } = TitleBarDecorations.All;
+
+        public bool ShowTitle
+        {
+            get => HasTitleBarDecoration(TitleBarDecorations.Title);
+            set => SetTitleBarDecoration(TitleBarDecorations.Title, value);
+        }
+
+        public bool ShowFullScreenButton
+        {
+            get => HasTitleBarDecoration(TitleBarDecorations.FullScreenButton);
+            set => SetTitleBarDecoration(TitleBarDecorations.FullScreenButton, value);
+        }
+
+        public bool ShowMinimizeButton
+        {
+            get => HasTitleBarDecoration(TitleBarDecorations.MinimizeButton);
+            set => SetTitleBarDecoration(TitleBarDecorations.MinimizeButton, value);
+        }
+
+        public bool ShowMaximizeButton
+        {
+            get => HasTitleBarDecoration(TitleBarDecorations.MaximizeButton);
+            set => SetTitleBarDecoration(TitleBarDecorations.MaximizeButton, value);
+        }
+
+        public bool ShowCloseButton
+        {
+            get => HasTitleBarDecoration(TitleBarDecorations.CloseButton);
+            set => SetTitleBarDecoration(TitleBarDecorations.CloseButton, value);
+        }
+
+        private bool HasTitleBarDecoration(TitleBarDecorations decoration)
+            => (TitleBarDecorations & decoration) != 0;
+
+        private void SetTitleBarDecoration(TitleBarDecorations decoration, bool value, [CallerMemberName] string? propertyName = null)
+        {
+            var newDecorations = value ? TitleBarDecorations | decoration : TitleBarDecorations & ~decoration;
+            if (newDecorations == TitleBarDecorations)
+                return;
+
+            TitleBarDecorations = newDecorations;
+            RaisePropertyChanged(propertyName);
+            RaisePropertyChanged(nameof(TitleBarDecorations));
+        }
+
         public MiniCommand AboutCommand { get; }
 
         public MiniCommand ExitCommand { get; }
diff --git a/src/Avalonia.Controls/Chrome/TitleBarDecorations.cs b/src/Avalonia.Controls/Chrome/TitleBarDecorations.cs
new file mode 100644
index 0000000000..dffa8c23d0
--- /dev/null
+++ b/src/Avalonia.Controls/Chrome/TitleBarDecorations.cs
@@ -0,0 +1,45 @@
+using System;
+
+namespace Avalonia.Controls.Chrome;
+
+/// <summary>
+/// Flags specifying which elements are displayed in a drawn window title bar of <see cref="WindowDrawnDecorations"/>.
+/// </summary>
+[Flags]
+public enum TitleBarDecorations
+{
+    /// <summary>
+    /// No title bar element is displayed.
+    /// </summary>
+    None = 0,
+
+    /// <summary>
+    /// The window title is displayed.
+    /// </summary>
+    Title = 1 << 0,
+
+    /// <summary>
+    /// The minimize button is displayed.
+    /// </summary>
+    MinimizeButton = 1 << 1,
+
+    /// <summary>
+    /// The maximize button is displayed.
+    /// </summary>
+    MaximizeButton = 1 << 2,
+
+    /// <summary>
+    /// The close button is displayed.
+    /// </summary>
+    CloseButton = 1 << 3,
+
+    /// <summary>
+    /// The full screen button is displayed.
+    /// </summary>
+    FullScreenButton = 1 << 4,
+
+    /// <summary>
+    /// All title bar elements are displayed.
+    /// </summary>
+    All = Title | MinimizeButton | MaximizeButton | CloseButton | FullScreenButton
+}
diff --git a/src/Avalonia.Controls/Chrome/WindowDrawnDecorations.cs b/src/Avalonia.Controls/Chrome/WindowDrawnDecorations.cs
index 26dffa8f5d..6cb17e59b9 100644
--- a/src/Avalonia.Controls/Chrome/WindowDrawnDecorations.cs
+++ b/src/Avalonia.Controls/Chrome/WindowDrawnDecorations.cs
@@ -17,7 +17,7 @@ namespace Avalonia.Controls.Chrome;
 /// and inserts them into its own visual tree.
 /// </summary>
 [PseudoClasses(pcNormal, pcMaximized, pcFullscreen, pcHasShadow, pcHasBorder, pcHasTitlebar,
-    pcHasMaximize, pcHasFullscreen, pcHasMinimize)]
+    pcHasMaximize, pcHasFullscreen, pcHasMinimize, pcHasClose, pcHasTitle)]
 [TemplatePart(PART_CloseButton, typeof(Button))]
 [TemplatePart(PART_MinimizeButton, typeof(Button))]
 [TemplatePart(PART_MaximizeButton, typeof(Button))]
@@ -36,6 +36,8 @@ public class WindowDrawnDecorations : StyledElement
     internal const string pcHasMaximize = ":has-maximize";
     internal const string pcHasFullscreen = ":has-fullscreen";
     internal const string pcHasMinimize = ":has-minimize";
+    internal const string pcHasClose = ":has-close";
+    internal const string pcHasTitle = ":has-title";
 
     // Template part names for caption buttons
     internal const string PART_CloseButton = "PART_CloseButton";
@@ -126,6 +128,13 @@ public class WindowDrawnDecorations : StyledElement
     public static readonly StyledProperty<string?> TitleProperty =
         AvaloniaProperty.Register<WindowDrawnDecorations, string?>(nameof(Title));
 
+    /// <summary>
+    /// Defines the TitleBarDecorations attached property.
+    /// </summary>
+    public static readonly AttachedProperty<TitleBarDecorations> TitleBarDecorationsProperty =
+        AvaloniaProperty.RegisterAttached<WindowDrawnDecorations, StyledElement, TitleBarDecorations>(
+            "TitleBarDecorations", TitleBarDecorations.All);
+
     /// <summary>
     /// Defines the <see cref="EnabledParts"/> property.
     /// </summary>
@@ -244,6 +253,7 @@ public class WindowDrawnDecorations : StyledElement
 
     /// <summary>
     /// Gets or sets the window title displayed in the decorations.
+    /// Mirrors the value set on the host <see cref="Window"/>.
     /// </summary>
     public string? Title
     {
@@ -251,6 +261,31 @@ public class WindowDrawnDecorations : StyledElement
         set => SetValue(TitleProperty, value);
     }
 
+    /// <summary>
+    /// Gets which title bar elements to display.
+    /// </summary>
+    public static TitleBarDecorations GetTitleBarDecorations(StyledElement element)
+        => element.GetValue(TitleBarDecorationsProperty);
+
+    /// <summary>
+    /// Sets which title bar elements to display.
+    /// </summary>
+    /// <remarks>
+    /// Set this property on a <see cref="Window"/> to control the elements displayed in its drawn title bar.
+    /// </remarks>
+    public static void SetTitleBarDecorations(StyledElement element, TitleBarDecorations value)
+        => element.SetValue(TitleBarDecorationsProperty, value);
+
+    /// <summary>
+    /// Gets or sets which title bar elements are requested to be displayed.
+    /// Mirrors the value set on the host <see cref="Window"/>.
+    /// </summary>
+    public TitleBarDecorations TitleBarDecorations
+    {
+        get => GetValue(TitleBarDecorationsProperty);
+        set => SetValue(TitleBarDecorationsProperty, value);
+    }
+
     /// <summary>
     /// Gets or sets which decoration parts are enabled.
     /// Set by Window based on platform capabilities and user preferences.
@@ -334,6 +369,7 @@ public class WindowDrawnDecorations : StyledElement
             x.UpdateEffectiveGeometry();
         });
 
+        TitleBarDecorationsProperty.Changed.AddClassHandler<WindowDrawnDecorations>((x, _) => x.UpdateTitleBarDecorationsPseudoClasses());
         DefaultTitleBarHeightProperty.Changed.AddClassHandler<WindowDrawnDecorations>((x, _) => x.UpdateEffectiveGeometry());
         DefaultFrameThicknessProperty.Changed.AddClassHandler<WindowDrawnDecorations>((x, _) => x.UpdateEffectiveGeometry());
         DefaultShadowThicknessProperty.Changed.AddClassHandler<WindowDrawnDecorations>((x, _) => x.UpdateEffectiveGeometry());
@@ -395,6 +431,8 @@ public class WindowDrawnDecorations : StyledElement
             Disposable.Create(() => window.AllowedWindowActionsChanged -= OnAllowedWindowActionsChanged),
             window.GetObservable(Window.TitleProperty)
                 .Subscribe(title => SetCurrentValue(TitleProperty, title)),
+            window.GetObservable(TitleBarDecorationsProperty)
+                .Subscribe(hints => SetCurrentValue(TitleBarDecorationsProperty, hints)),
             window.GetObservable(Window.CanMaximizeProperty)
                 .Subscribe(_ =>
                 {
@@ -415,7 +453,7 @@ public class WindowDrawnDecorations : StyledElement
                 }),
         };
 
-        UpdateAllowedActionsPseudoClasses();
+        UpdateTitleBarDecorationsPseudoClasses();
         UpdateMaximizeButtonState();
         UpdateMinimizeButtonState();
         UpdateFullScreenButtonState();
@@ -592,18 +630,25 @@ public class WindowDrawnDecorations : StyledElement
 
     private void OnAllowedWindowActionsChanged(PlatformAllowedWindowActions actions)
     {
-        UpdateAllowedActionsPseudoClasses();
+        UpdateTitleBarDecorationsPseudoClasses();
         UpdateMaximizeButtonState();
         UpdateMinimizeButtonState();
         UpdateFullScreenButtonState();
     }
 
-    private void UpdateAllowedActionsPseudoClasses()
+    private void UpdateTitleBarDecorationsPseudoClasses()
     {
         var actions = EffectiveAllowedActions;
-        PseudoClasses.Set(pcHasMaximize, actions.HasFlag(PlatformAllowedWindowActions.Maximize));
-        PseudoClasses.Set(pcHasFullscreen, actions.HasFlag(PlatformAllowedWindowActions.Fullscreen));
-        PseudoClasses.Set(pcHasMinimize, actions.HasFlag(PlatformAllowedWindowActions.Minimize));
+        var hints = TitleBarDecorations;
+
+        PseudoClasses.Set(pcHasMaximize, actions.HasFlag(PlatformAllowedWindowActions.Maximize)
+                                         && hints.HasFlag(TitleBarDecorations.MaximizeButton));
+        PseudoClasses.Set(pcHasFullscreen, actions.HasFlag(PlatformAllowedWindowActions.Fullscreen)
+                                           && hints.HasFlag(TitleBarDecorations.FullScreenButton));
+        PseudoClasses.Set(pcHasMinimize, actions.HasFlag(PlatformAllowedWindowActions.Minimize)
+                                         && hints.HasFlag(TitleBarDecorations.MinimizeButton));
+        PseudoClasses.Set(pcHasClose, hints.HasFlag(TitleBarDecorations.CloseButton));
+        PseudoClasses.Set(pcHasTitle, hints.HasFlag(TitleBarDecorations.Title));
     }
 
     private void UpdateEffectiveGeometry()
diff --git a/src/Avalonia.Themes.Fluent/Controls/WindowDrawnDecorations.xaml b/src/Avalonia.Themes.Fluent/Controls/WindowDrawnDecorations.xaml
index d9af9faf79..2c4969f212 100644
--- a/src/Avalonia.Themes.Fluent/Controls/WindowDrawnDecorations.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/WindowDrawnDecorations.xaml
@@ -128,7 +128,8 @@
                    VerticalAlignment="Top"
                    Background="{DynamicResource SystemControlBackgroundChromeMediumLowBrush}"
                    WindowDecorationProperties.ElementRole="TitleBar">
-              <TextBlock Text="{TemplateBinding Title}"
+              <TextBlock x:Name="PART_PopoverTitleText"
+                         Text="{TemplateBinding Title}"
                          VerticalAlignment="Center"
                          Margin="12,0,0,0"
                          FontSize="12" />
@@ -196,7 +197,8 @@
       <Setter Property="Opacity" Value="0.2"/>
     </Style>
 
-    <!-- Hide caption buttons when the platform does not support the action -->
+    <!-- Hide title bar elements when the platform does not support the action
+         or when they aren't requested by WindowDrawnDecorations.TitleBarDecorationHints -->
     <Style Selector="^:not(:has-minimize) /template/ Button#PART_MinimizeButton">
       <Setter Property="IsVisible" Value="False"/>
     </Style>
@@ -209,6 +211,18 @@
     <Style Selector="^:not(:has-fullscreen) /template/ Button#PART_PopoverFullScreenButton">
       <Setter Property="IsVisible" Value="False"/>
     </Style>
+    <Style Selector="^:not(:has-close) /template/ Button#PART_CloseButton">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-close) /template/ Button#PART_PopoverCloseButton">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-title) /template/ Panel#PART_TitleTextPanel">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-title) /template/ TextBlock#PART_PopoverTitleText">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
 
     <!-- Fullscreen: hide overlay and titlebar (popover takes over) -->
     <Style Selector="^:fullscreen /template/ Panel#PART_TitleTextPanel">
diff --git a/src/Avalonia.Themes.Simple/Controls/WindowDrawnDecorations.xaml b/src/Avalonia.Themes.Simple/Controls/WindowDrawnDecorations.xaml
index 3d76f8b277..acfba2e23e 100644
--- a/src/Avalonia.Themes.Simple/Controls/WindowDrawnDecorations.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/WindowDrawnDecorations.xaml
@@ -131,7 +131,8 @@
                    VerticalAlignment="Top"
                    Background="{DynamicResource ThemeAccentBrush}"
                    WindowDecorationProperties.ElementRole="TitleBar">
-              <TextBlock Text="{TemplateBinding Title}"
+              <TextBlock x:Name="PART_PopoverTitleText"
+                         Text="{TemplateBinding Title}"
                          VerticalAlignment="Center"
                          Foreground="White"
                          Margin="12,0,0,0"
@@ -202,7 +203,8 @@
       <Setter Property="Opacity" Value="0.2"/>
     </Style>
 
-    <!-- Hide caption buttons when the platform does not support the action -->
+    <!-- Hide title bar elements when the platform does not support the action
+         or when they aren't requested by WindowDrawnDecorations.TitleBarDecorationHints -->
     <Style Selector="^:not(:has-minimize) /template/ Button#PART_MinimizeButton">
       <Setter Property="IsVisible" Value="False"/>
     </Style>
@@ -215,6 +217,18 @@
     <Style Selector="^:not(:has-fullscreen) /template/ Button#PART_PopoverFullScreenButton">
       <Setter Property="IsVisible" Value="False"/>
     </Style>
+    <Style Selector="^:not(:has-close) /template/ Button#PART_CloseButton">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-close) /template/ Button#PART_PopoverCloseButton">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-title) /template/ Panel#PART_TitleTextPanel">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
+    <Style Selector="^:not(:has-title) /template/ TextBlock#PART_PopoverTitleText">
+      <Setter Property="IsVisible" Value="False"/>
+    </Style>
 
     <!-- Fullscreen: hide overlay and titlebar (popover takes over) -->
     <Style Selector="^:fullscreen /template/ Panel#PART_TitleTextPanel">
diff --git a/tests/Avalonia.Controls.UnitTests/WindowTests.cs b/tests/Avalonia.Controls.UnitTests/WindowTests.cs
index 646dad30ec..ebd07d2596 100644
--- a/tests/Avalonia.Controls.UnitTests/WindowTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/WindowTests.cs
@@ -1642,6 +1642,98 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        public class TitleBarDecorationsTests : ScopedTestBase
+        {
+            private static Window CreateWindowWithDrawnDecorations(PlatformAllowedWindowActions allowedActions = PlatformAllowedWindowActions.All)
+            {
+                var windowImpl = MockWindowingPlatform.CreateWindowMock();
+                windowImpl.Setup(x => x.NeedsManagedDecorations).Returns(true);
+                windowImpl.Setup(x => x.RequestedDrawnDecorations).Returns(
+                    PlatformRequestedDrawnDecoration.TitleBar | PlatformRequestedDrawnDecoration.Border);
+                windowImpl.Setup(x => x.AllowedWindowActions).Returns(allowedActions);
+
+                return new Window(windowImpl.Object);
+            }
+
+            private static void AssertClassDecorations(WindowDrawnDecorations drawnDecorations, TitleBarDecorations expected)
+            {
+                AssertClassDecoration(TitleBarDecorations.Title, ":has-title");
+                AssertClassDecoration(TitleBarDecorations.MinimizeButton, ":has-minimize");
+                AssertClassDecoration(TitleBarDecorations.MaximizeButton, ":has-maximize");
+                AssertClassDecoration(TitleBarDecorations.CloseButton, ":has-close");
+                AssertClassDecoration(TitleBarDecorations.FullScreenButton, ":has-fullscreen");
+
+                void AssertClassDecoration(TitleBarDecorations decoration, string className)
+                    => Assert.Equal(expected.HasFlag(decoration), drawnDecorations.Classes.Contains(className));
+            }
+
+            [Fact]
+            public void All_Decorations_Should_Be_Visible_By_Default()
+            {
+                using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+                var window = CreateWindowWithDrawnDecorations();
+                window.Show();
+
+                var decorations = window.TopLevelHost.Decorations;
+                Assert.NotNull(decorations);
+                Assert.Equal(TitleBarDecorations.All, decorations.TitleBarDecorations);
+                AssertClassDecorations(decorations, TitleBarDecorations.All);
+            }
+
+            [Fact]
+            public void Decorations_Set_Before_Show_Should_Apply_Correct_Classes()
+            {
+                using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+                const TitleBarDecorations decorations = TitleBarDecorations.Title | TitleBarDecorations.CloseButton;
+
+                var window = CreateWindowWithDrawnDecorations();
+                WindowDrawnDecorations.SetTitleBarDecorations(window, decorations);
+                window.Show();
+
+                var drawnDecorations = window.TopLevelHost.Decorations;
+                Assert.NotNull(drawnDecorations);
+                Assert.Equal(decorations, drawnDecorations.TitleBarDecorations);
+                AssertClassDecorations(drawnDecorations, decorations);
+            }
+
+            [Fact]
+            public void Decorations_Set_After_Show_Should_Apply_Correct_Classes()
+            {
+                using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+                var window = CreateWindowWithDrawnDecorations();
+                window.Show();
+
+                var drawnDecorations = window.TopLevelHost.Decorations;
+                Assert.NotNull(drawnDecorations);
+
+                WindowDrawnDecorations.SetTitleBarDecorations(window, TitleBarDecorations.None);
+                AssertClassDecorations(drawnDecorations, TitleBarDecorations.None);
+
+                WindowDrawnDecorations.SetTitleBarDecorations(window, TitleBarDecorations.MinimizeButton);
+                AssertClassDecorations(drawnDecorations, TitleBarDecorations.MinimizeButton);
+            }
+
+            [Fact]
+            public void Decorations_Should_Not_Show_Buttons_Unsupported_By_The_Platform()
+            {
+                using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+                var window = CreateWindowWithDrawnDecorations(PlatformAllowedWindowActions.Minimize);
+                window.Show();
+
+                var decorations = window.TopLevelHost.Decorations;
+                Assert.NotNull(decorations);
+
+                // Maximize and fullscreen are requested, but not allowed by the platform.
+                AssertClassDecorations(
+                    decorations,
+                    TitleBarDecorations.Title | TitleBarDecorations.MinimizeButton | TitleBarDecorations.CloseButton);
+            }
+        }
+
         private class TopmostWindow : Window
         {
             static TopmostWindow()