diff --git a/samples/ControlCatalog/Converter/HexConverter.cs b/samples/ControlCatalog/Converter/HexConverter.cs
index 83a52212f6..31cce5ba67 100644
--- a/samples/ControlCatalog/Converter/HexConverter.cs
+++ b/samples/ControlCatalog/Converter/HexConverter.cs
@@ -7,7 +7,7 @@ namespace ControlCatalog.Converter;
 
 public class HexConverter : IValueConverter
 {
-    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {
         var str = value?.ToString();
         if (str == null)
@@ -18,7 +18,7 @@ public class HexConverter : IValueConverter
 
     }
 
-    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
     {
         try
         {
diff --git a/src/Avalonia.Base/Layout/LayoutHelper.cs b/src/Avalonia.Base/Layout/LayoutHelper.cs
index 404d19906a..0851dbaea9 100644
--- a/src/Avalonia.Base/Layout/LayoutHelper.cs
+++ b/src/Avalonia.Base/Layout/LayoutHelper.cs
@@ -251,6 +251,17 @@ namespace Avalonia.Layout
         {
             double newValue;
 
+            // Round the value to avoid FP errors. This is needed because if `value` has a floating
+            // point precision error (e.g. 79.333333333333343) then when it's multiplied by
+            // `dpiScale` and rounded up, it will be rounded up to a value one greater than it
+            // should be.
+#if NET6_0_OR_GREATER
+            value = Math.Round(value, 8, MidpointRounding.ToZero);
+#else
+            // MidpointRounding.ToZero isn't available in netstandard2.0.
+            value = Math.Truncate(value * 1e8) / 1e8;
+#endif
+
             // If DPI == 1, don't use DPI-aware rounding.
             if (!MathUtilities.IsOne(dpiScale))
             {
diff --git a/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs b/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs
new file mode 100644
index 0000000000..421a5acb28
--- /dev/null
+++ b/src/Avalonia.Controls.ColorPicker/Converters/DoNothingForNullConverter.cs
@@ -0,0 +1,35 @@
+using System;
+using System.Globalization;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+
+namespace Avalonia.Controls.Converters
+{
+    /// <summary>
+    /// Converter that will do nothing (not update bound values) when a null value is encountered.
+    /// This converter enables binding nullable with non-nullable properties in some scenarios.
+    /// </summary>
+    public class DoNothingForNullConverter : IValueConverter
+    {
+        /// <inheritdoc/>
+        public object? Convert(
+            object? value,
+            Type targetType,
+            object? parameter,
+            CultureInfo culture)
+        {
+            return value ?? BindingOperations.DoNothing;
+        }
+
+        /// <inheritdoc/>
+        public object? ConvertBack(
+            object? value,
+            Type targetType,
+            object? parameter,
+            CultureInfo culture)
+        {
+            return value ?? BindingOperations.DoNothing;
+        }
+    }
+}
+
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
index 59cc48975f..dab4142001 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
@@ -11,6 +11,7 @@
   <pc:ThirdComponentConverter x:Key="ThirdComponentConverter" />
   <converters:ColorToDisplayNameConverter x:Key="ColorToDisplayNameConverter" />
   <converters:ColorToHexConverter x:Key="ColorToHexConverter" />
+  <converters:DoNothingForNullConverter x:Key="DoNothingForNullConverter" />
   <globalization:NumberFormatInfo x:Key="ColorViewComponentNumberFormat" NumberDecimalDigits="0" />
   <x:Double x:Key="ColorViewTabStripHeight">48</x:Double>
   <x:Double x:Key="ColorViewComponentLabelWidth">30</x:Double>
@@ -205,7 +206,7 @@
                 </Border>
               </TabItem.Header>
               <ListBox Items="{TemplateBinding PaletteColors}"
-                       SelectedItem="{Binding Color, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"
+                       SelectedItem="{Binding Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource DoNothingForNullConverter}, Mode=TwoWay}"
                        UseLayoutRounding="False"
                        Margin="12">
                 <ListBox.Styles>
diff --git a/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs b/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
index d63c738133..69e6766bfd 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridRowGroupHeader.cs
@@ -23,10 +23,10 @@ namespace Avalonia.Controls
     [PseudoClasses(":pressed", ":current", ":expanded")]
     public class DataGridRowGroupHeader : TemplatedControl
     {
-        private const string DATAGRIDROWGROUPHEADER_expanderButton = "ExpanderButton";
-        private const string DATAGRIDROWGROUPHEADER_indentSpacer = "IndentSpacer";
-        private const string DATAGRIDROWGROUPHEADER_itemCountElement = "ItemCountElement";
-        private const string DATAGRIDROWGROUPHEADER_propertyNameElement = "PropertyNameElement";
+        private const string DATAGRIDROWGROUPHEADER_expanderButton = "PART_ExpanderButton";
+        private const string DATAGRIDROWGROUPHEADER_indentSpacer = "PART_IndentSpacer";
+        private const string DATAGRIDROWGROUPHEADER_itemCountElement = "PART_ItemCountElement";
+        private const string DATAGRIDROWGROUPHEADER_propertyNameElement = "PART_PropertyNameElement";
 
         private bool _areIsCheckedHandlersSuspended;
         private ToggleButton _expanderButton;
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
index 364a2a52e3..b4bae02b9b 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
@@ -409,9 +409,9 @@
                               ColumnDefinitions="Auto,Auto,Auto,Auto,*"
                               RowDefinitions="*,Auto">
 
-            <Rectangle Name="IndentSpacer"
+            <Rectangle Name="PART_IndentSpacer"
                        Grid.Column="1" />
-            <ToggleButton Name="ExpanderButton"
+            <ToggleButton Name="PART_ExpanderButton"
                           Grid.Column="2"
                           Width="12"
                           Height="12"
@@ -428,14 +428,14 @@
                         Orientation="Horizontal"
                         VerticalAlignment="Center"
                         Margin="12,0,0,0">
-              <TextBlock Name="PropertyNameElement"
+              <TextBlock Name="PART_PropertyNameElement"
                          Margin="4,0,0,0"
                          IsVisible="{TemplateBinding IsPropertyNameVisible}"
                          Foreground="{TemplateBinding Foreground}" />
               <TextBlock Margin="4,0,0,0"
                          Text="{ReflectionBinding Key}"
                          Foreground="{TemplateBinding Foreground}" />
-              <TextBlock Name="ItemCountElement"
+              <TextBlock Name="PART_ItemCountElement"
                          Margin="4,0,0,0"
                          IsVisible="{TemplateBinding IsItemCountVisible}"
                          Foreground="{TemplateBinding Foreground}" />
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml b/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
index 6a748f399e..b43addff86 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
@@ -258,10 +258,10 @@
                               ColumnDefinitions="Auto,Auto,Auto,Auto"
                               RowDefinitions="Auto,*,Auto">
 
-            <Rectangle Name="IndentSpacer"
+            <Rectangle Name="PART_IndentSpacer"
                        Grid.Row="1"
                        Grid.Column="1" />
-            <ToggleButton Name="ExpanderButton"
+            <ToggleButton Name="PART_ExpanderButton"
                           Grid.Row="1"
                           Grid.Column="2"
                           Margin="2,0,0,0"
@@ -277,12 +277,12 @@
                         Margin="0,1,0,1"
                         VerticalAlignment="Center"
                         Orientation="Horizontal">
-              <TextBlock Name="PropertyNameElement"
+              <TextBlock Name="PART_PropertyNameElement"
                          Margin="4,0,0,0"
                          IsVisible="{TemplateBinding IsPropertyNameVisible}" />
               <TextBlock Margin="4,0,0,0"
                          Text="{Binding Key}" />
-              <TextBlock Name="ItemCountElement"
+              <TextBlock Name="PART_ItemCountElement"
                          Margin="4,0,0,0"
                          IsVisible="{TemplateBinding IsItemCountVisible}" />
             </StackPanel>
diff --git a/src/Avalonia.Controls/Calendar/Calendar.cs b/src/Avalonia.Controls/Calendar/Calendar.cs
index bb838a4f3f..0de068a416 100644
--- a/src/Avalonia.Controls/Calendar/Calendar.cs
+++ b/src/Avalonia.Controls/Calendar/Calendar.cs
@@ -2109,8 +2109,8 @@ namespace Avalonia.Controls
             RemovedItems = new Collection<DateTime>();
         }
 
-        private const string PART_ElementRoot = "Root";
-        private const string PART_ElementMonth = "CalendarItem";
+        private const string PART_ElementRoot = "PART_Root";
+        private const string PART_ElementMonth = "PART_CalendarItem";
 
         /// <summary>
         /// Builds the visual tree for the
diff --git a/src/Avalonia.Controls/Calendar/CalendarItem.cs b/src/Avalonia.Controls/Calendar/CalendarItem.cs
index 75e9f52621..e2eabb5f28 100644
--- a/src/Avalonia.Controls/Calendar/CalendarItem.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarItem.cs
@@ -32,11 +32,11 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         private const int NumberOfDaysPerWeek = 7;
 
-        private const string PART_ElementHeaderButton = "HeaderButton";
-        private const string PART_ElementPreviousButton = "PreviousButton";
-        private const string PART_ElementNextButton = "NextButton";
-        private const string PART_ElementMonthView = "MonthView";
-        private const string PART_ElementYearView = "YearView";
+        private const string PART_ElementHeaderButton = "PART_HeaderButton";
+        private const string PART_ElementPreviousButton = "PART_PreviousButton";
+        private const string PART_ElementNextButton = "PART_NextButton";
+        private const string PART_ElementMonthView = "PART_MonthView";
+        private const string PART_ElementYearView = "PART_YearView";
 
         private Button? _headerButton;
         private Button? _nextButton;
diff --git a/src/Avalonia.Controls/DateTimePickers/DatePicker.cs b/src/Avalonia.Controls/DateTimePickers/DatePicker.cs
index f2b808fe0d..fb27feb521 100644
--- a/src/Avalonia.Controls/DateTimePickers/DatePicker.cs
+++ b/src/Avalonia.Controls/DateTimePickers/DatePicker.cs
@@ -14,15 +14,15 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control to allow the user to select a date
     /// </summary>
-    [TemplatePart("ButtonContentGrid", typeof(Grid))]
-    [TemplatePart("DayText",           typeof(TextBlock))]
-    [TemplatePart("FirstSpacer",       typeof(Rectangle))]
-    [TemplatePart("FlyoutButton",      typeof(Button))]
-    [TemplatePart("MonthText",         typeof(TextBlock))]
-    [TemplatePart("PickerPresenter",   typeof(DatePickerPresenter))]
-    [TemplatePart("Popup",             typeof(Popup))]
-    [TemplatePart("SecondSpacer",      typeof(Rectangle))]
-    [TemplatePart("YearText",          typeof(TextBlock))]
+    [TemplatePart("PART_ButtonContentGrid", typeof(Grid))]
+    [TemplatePart("PART_DayTextBlock",      typeof(TextBlock))]
+    [TemplatePart("PART_FirstSpacer",       typeof(Rectangle))]
+    [TemplatePart("PART_FlyoutButton",      typeof(Button))]
+    [TemplatePart("PART_MonthTextBlock",    typeof(TextBlock))]
+    [TemplatePart("PART_PickerPresenter",   typeof(DatePickerPresenter))]
+    [TemplatePart("PART_Popup",             typeof(Popup))]
+    [TemplatePart("PART_SecondSpacer",      typeof(Rectangle))]
+    [TemplatePart("PART_YearTextBlock",     typeof(TextBlock))]
     [PseudoClasses(":hasnodate")]
     public class DatePicker : TemplatedControl
     {
@@ -280,15 +280,15 @@ namespace Avalonia.Controls
             }
 
             base.OnApplyTemplate(e);
-            _flyoutButton = e.NameScope.Find<Button>("FlyoutButton");
-            _dayText = e.NameScope.Find<TextBlock>("DayText");
-            _monthText = e.NameScope.Find<TextBlock>("MonthText");
-            _yearText = e.NameScope.Find<TextBlock>("YearText");
-            _container = e.NameScope.Find<Grid>("ButtonContentGrid");
-            _spacer1 = e.NameScope.Find<Rectangle>("FirstSpacer");
-            _spacer2 = e.NameScope.Find<Rectangle>("SecondSpacer");
-            _popup = e.NameScope.Find<Popup>("Popup");
-            _presenter = e.NameScope.Find<DatePickerPresenter>("PickerPresenter");
+            _flyoutButton = e.NameScope.Find<Button>("PART_FlyoutButton");
+            _dayText = e.NameScope.Find<TextBlock>("PART_DayTextBlock");
+            _monthText = e.NameScope.Find<TextBlock>("PART_MonthTextBlock");
+            _yearText = e.NameScope.Find<TextBlock>("PART_YearTextBlock");
+            _container = e.NameScope.Find<Grid>("PART_ButtonContentGrid");
+            _spacer1 = e.NameScope.Find<Rectangle>("PART_FirstSpacer");
+            _spacer2 = e.NameScope.Find<Rectangle>("PART_SecondSpacer");
+            _popup = e.NameScope.Find<Popup>("PART_Popup");
+            _presenter = e.NameScope.Find<DatePickerPresenter>("PART_PickerPresenter");
 
             _areControlsAvailable = true;
 
diff --git a/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs b/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
index 0612efe14d..2057480490 100644
--- a/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
+++ b/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
@@ -13,23 +13,23 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a date for a 
     /// <see cref="DatePicker"/>
     /// </summary>
-    [TemplatePart("AcceptButton",    typeof(Button))]
-    [TemplatePart("DayDownButton",   typeof(RepeatButton))]
-    [TemplatePart("DayHost",         typeof(Panel))]
-    [TemplatePart("DaySelector",     typeof(DateTimePickerPanel))]
-    [TemplatePart("DayUpButton",     typeof(RepeatButton))]
-    [TemplatePart("DismissButton",   typeof(Button))]
-    [TemplatePart("FirstSpacer",     typeof(Rectangle))]
-    [TemplatePart("MonthDownButton", typeof(RepeatButton))]
-    [TemplatePart("MonthHost",       typeof(Panel))]
-    [TemplatePart("MonthSelector",   typeof(DateTimePickerPanel))]
-    [TemplatePart("MonthUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PickerContainer", typeof(Grid))]
-    [TemplatePart("SecondSpacer",    typeof(Rectangle))]
-    [TemplatePart("YearDownButton",  typeof(RepeatButton))]
-    [TemplatePart("YearHost",        typeof(Panel))]
-    [TemplatePart("YearSelector",    typeof(DateTimePickerPanel))]
-    [TemplatePart("YearUpButton",    typeof(RepeatButton))]
+    [TemplatePart("PART_AcceptButton",    typeof(Button))]
+    [TemplatePart("PART_DayDownButton",   typeof(RepeatButton))]
+    [TemplatePart("PART_DayHost",         typeof(Panel))]
+    [TemplatePart("PART_DaySelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_DayUpButton",     typeof(RepeatButton))]
+    [TemplatePart("PART_DismissButton",   typeof(Button))]
+    [TemplatePart("PART_FirstSpacer",     typeof(Rectangle))]
+    [TemplatePart("PART_MonthDownButton", typeof(RepeatButton))]
+    [TemplatePart("PART_MonthHost",       typeof(Panel))]
+    [TemplatePart("PART_MonthSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MonthUpButton",   typeof(RepeatButton))]
+    [TemplatePart("PART_PickerContainer", typeof(Grid))]
+    [TemplatePart("PART_SecondSpacer",    typeof(Rectangle))]
+    [TemplatePart("PART_YearDownButton",  typeof(RepeatButton))]
+    [TemplatePart("PART_YearHost",        typeof(Panel))]
+    [TemplatePart("PART_YearSelector",    typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_YearUpButton",    typeof(RepeatButton))]
     public class DatePickerPresenter : PickerPresenterBase
     {
         /// <summary>
@@ -253,58 +253,58 @@ namespace Avalonia.Controls
         {
             base.OnApplyTemplate(e);
             // These are requirements, so throw if not found
-            _pickerContainer = e.NameScope.Get<Grid>("PickerContainer");
-            _monthHost = e.NameScope.Get<Panel>("MonthHost");
-            _dayHost = e.NameScope.Get<Panel>("DayHost");
-            _yearHost = e.NameScope.Get<Panel>("YearHost");
+            _pickerContainer = e.NameScope.Get<Grid>("PART_PickerContainer");
+            _monthHost = e.NameScope.Get<Panel>("PART_MonthHost");
+            _dayHost = e.NameScope.Get<Panel>("PART_DayHost");
+            _yearHost = e.NameScope.Get<Panel>("PART_YearHost");
 
-            _monthSelector = e.NameScope.Get<DateTimePickerPanel>("MonthSelector");
+            _monthSelector = e.NameScope.Get<DateTimePickerPanel>("PART_MonthSelector");
             _monthSelector.SelectionChanged += OnMonthChanged;
 
-            _daySelector = e.NameScope.Get<DateTimePickerPanel>("DaySelector");
+            _daySelector = e.NameScope.Get<DateTimePickerPanel>("PART_DaySelector");
             _daySelector.SelectionChanged += OnDayChanged;
 
-            _yearSelector = e.NameScope.Get<DateTimePickerPanel>("YearSelector");
+            _yearSelector = e.NameScope.Get<DateTimePickerPanel>("PART_YearSelector");
             _yearSelector.SelectionChanged += OnYearChanged;
 
-            _acceptButton = e.NameScope.Get<Button>("AcceptButton");
+            _acceptButton = e.NameScope.Get<Button>("PART_AcceptButton");
 
-            _monthUpButton = e.NameScope.Find<RepeatButton>("MonthUpButton");
+            _monthUpButton = e.NameScope.Find<RepeatButton>("PART_MonthUpButton");
             if (_monthUpButton != null)
             {
                 _monthUpButton.Click += OnSelectorButtonClick;
             }
-            _monthDownButton = e.NameScope.Find<RepeatButton>("MonthDownButton");
+            _monthDownButton = e.NameScope.Find<RepeatButton>("PART_MonthDownButton");
             if (_monthDownButton != null)
             {
                 _monthDownButton.Click += OnSelectorButtonClick;
             }
 
-            _dayUpButton = e.NameScope.Find<RepeatButton>("DayUpButton");
+            _dayUpButton = e.NameScope.Find<RepeatButton>("PART_DayUpButton");
             if (_dayUpButton != null)
             {
                 _dayUpButton.Click += OnSelectorButtonClick;
             }
-            _dayDownButton = e.NameScope.Find<RepeatButton>("DayDownButton");
+            _dayDownButton = e.NameScope.Find<RepeatButton>("PART_DayDownButton");
             if (_dayDownButton != null)
             {
                 _dayDownButton.Click += OnSelectorButtonClick;
             }
 
-            _yearUpButton = e.NameScope.Find<RepeatButton>("YearUpButton");
+            _yearUpButton = e.NameScope.Find<RepeatButton>("PART_YearUpButton");
             if (_yearUpButton != null)
             {
                 _yearUpButton.Click += OnSelectorButtonClick;
             }
-            _yearDownButton = e.NameScope.Find<RepeatButton>("YearDownButton");
+            _yearDownButton = e.NameScope.Find<RepeatButton>("PART_YearDownButton");
             if (_yearDownButton != null)
             {
                 _yearDownButton.Click += OnSelectorButtonClick;
             }
 
-            _dismissButton = e.NameScope.Find<Button>("DismissButton");
-            _spacer1 = e.NameScope.Find<Rectangle>("FirstSpacer");
-            _spacer2 = e.NameScope.Find<Rectangle>("SecondSpacer");
+            _dismissButton = e.NameScope.Find<Button>("PART_DismissButton");
+            _spacer1 = e.NameScope.Find<Rectangle>("PART_FirstSpacer");
+            _spacer2 = e.NameScope.Find<Rectangle>("PART_SecondSpacer");
 
             if (_acceptButton != null)
             {
diff --git a/src/Avalonia.Controls/DateTimePickers/TimePicker.cs b/src/Avalonia.Controls/DateTimePickers/TimePicker.cs
index 047667567d..a709e4fb49 100644
--- a/src/Avalonia.Controls/DateTimePickers/TimePicker.cs
+++ b/src/Avalonia.Controls/DateTimePickers/TimePicker.cs
@@ -12,18 +12,18 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control to allow the user to select a time.
     /// </summary>
-    [TemplatePart("FirstColumnDivider",      typeof(Rectangle))]
-    [TemplatePart("FirstPickerHost",         typeof(Border))]
-    [TemplatePart("FlyoutButton",            typeof(Button))]
-    [TemplatePart("FlyoutButtonContentGrid", typeof(Grid))]
-    [TemplatePart("HourTextBlock",           typeof(TextBlock))]
-    [TemplatePart("MinuteTextBlock",         typeof(TextBlock))]
-    [TemplatePart("PeriodTextBlock",         typeof(TextBlock))]
-    [TemplatePart("PickerPresenter",         typeof(TimePickerPresenter))]
-    [TemplatePart("Popup",                   typeof(Popup))]
-    [TemplatePart("SecondColumnDivider",     typeof(Rectangle))]
-    [TemplatePart("SecondPickerHost",        typeof(Border))]
-    [TemplatePart("ThirdPickerHost",         typeof(Border))]
+    [TemplatePart("PART_FirstColumnDivider",      typeof(Rectangle))]
+    [TemplatePart("PART_FirstPickerHost",         typeof(Border))]
+    [TemplatePart("PART_FlyoutButton",            typeof(Button))]
+    [TemplatePart("PART_FlyoutButtonContentGrid", typeof(Grid))]
+    [TemplatePart("PART_HourTextBlock",           typeof(TextBlock))]
+    [TemplatePart("PART_MinuteTextBlock",         typeof(TextBlock))]
+    [TemplatePart("PART_PeriodTextBlock",         typeof(TextBlock))]
+    [TemplatePart("PART_PickerPresenter",         typeof(TimePickerPresenter))]
+    [TemplatePart("PART_Popup",                   typeof(Popup))]
+    [TemplatePart("PART_SecondColumnDivider",     typeof(Rectangle))]
+    [TemplatePart("PART_SecondPickerHost",        typeof(Border))]
+    [TemplatePart("PART_ThirdPickerHost",         typeof(Border))]
     [PseudoClasses(":hasnotime")]
     public class TimePicker : TemplatedControl
     {
@@ -169,23 +169,23 @@ namespace Avalonia.Controls
             }
             base.OnApplyTemplate(e);
 
-            _flyoutButton = e.NameScope.Find<Button>("FlyoutButton");
+            _flyoutButton = e.NameScope.Find<Button>("PART_FlyoutButton");
 
-            _firstPickerHost = e.NameScope.Find<Border>("FirstPickerHost");
-            _secondPickerHost = e.NameScope.Find<Border>("SecondPickerHost");
-            _thirdPickerHost = e.NameScope.Find<Border>("ThirdPickerHost");
+            _firstPickerHost = e.NameScope.Find<Border>("PART_FirstPickerHost");
+            _secondPickerHost = e.NameScope.Find<Border>("PART_SecondPickerHost");
+            _thirdPickerHost = e.NameScope.Find<Border>("PART_ThirdPickerHost");
 
-            _hourText = e.NameScope.Find<TextBlock>("HourTextBlock");
-            _minuteText = e.NameScope.Find<TextBlock>("MinuteTextBlock");
-            _periodText = e.NameScope.Find<TextBlock>("PeriodTextBlock");
+            _hourText = e.NameScope.Find<TextBlock>("PART_HourTextBlock");
+            _minuteText = e.NameScope.Find<TextBlock>("PART_MinuteTextBlock");
+            _periodText = e.NameScope.Find<TextBlock>("PART_PeriodTextBlock");
 
-            _firstSplitter = e.NameScope.Find<Rectangle>("FirstColumnDivider");
-            _secondSplitter = e.NameScope.Find<Rectangle>("SecondColumnDivider");
+            _firstSplitter = e.NameScope.Find<Rectangle>("PART_FirstColumnDivider");
+            _secondSplitter = e.NameScope.Find<Rectangle>("PART_SecondColumnDivider");
 
-            _contentGrid = e.NameScope.Find<Grid>("FlyoutButtonContentGrid");
+            _contentGrid = e.NameScope.Find<Grid>("PART_FlyoutButtonContentGrid");
 
-            _popup = e.NameScope.Find<Popup>("Popup");
-            _presenter = e.NameScope.Find<TimePickerPresenter>("PickerPresenter");
+            _popup = e.NameScope.Find<Popup>("PART_Popup");
+            _presenter = e.NameScope.Find<TimePickerPresenter>("PART_PickerPresenter");
 
             if (_flyoutButton != null)
                 _flyoutButton.Click += OnFlyoutButtonClicked;
diff --git a/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs b/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
index 46c5eaeaaa..d6599c9f18 100644
--- a/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
+++ b/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
@@ -11,20 +11,20 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a time. Intended for use with
     /// <see cref="TimePicker"/> but can be used independently
     /// </summary>
-    [TemplatePart("AcceptButton",     typeof(Button))]
-    [TemplatePart("DismissButton",    typeof(Button))]
-    [TemplatePart("HourDownButton",   typeof(RepeatButton))]
-    [TemplatePart("HourSelector",     typeof(DateTimePickerPanel))]
-    [TemplatePart("HourUpButton",     typeof(RepeatButton))]
-    [TemplatePart("MinuteDownButton", typeof(RepeatButton))]
-    [TemplatePart("MinuteSelector",   typeof(DateTimePickerPanel))]
-    [TemplatePart("MinuteUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PeriodDownButton", typeof(RepeatButton))]
-    [TemplatePart("PeriodHost",       typeof(Panel))]
-    [TemplatePart("PeriodSelector",   typeof(DateTimePickerPanel))]
-    [TemplatePart("PeriodUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PickerContainer",  typeof(Grid))]
-    [TemplatePart("SecondSpacer",     typeof(Rectangle))]
+    [TemplatePart("PART_AcceptButton",     typeof(Button))]
+    [TemplatePart("PART_DismissButton",    typeof(Button))]
+    [TemplatePart("PART_HourDownButton",   typeof(RepeatButton))]
+    [TemplatePart("PART_HourSelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_HourUpButton",     typeof(RepeatButton))]
+    [TemplatePart("PART_MinuteDownButton", typeof(RepeatButton))]
+    [TemplatePart("PART_MinuteSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MinuteUpButton",   typeof(RepeatButton))]
+    [TemplatePart("PART_PeriodDownButton", typeof(RepeatButton))]
+    [TemplatePart("PART_PeriodHost",       typeof(Panel))]
+    [TemplatePart("PART_PeriodSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_PeriodUpButton",   typeof(RepeatButton))]
+    [TemplatePart("PART_PickerContainer",  typeof(Grid))]
+    [TemplatePart("PART_SecondSpacer",     typeof(Rectangle))]
     public class TimePickerPresenter : PickerPresenterBase
     {
         /// <summary>
@@ -122,40 +122,40 @@ namespace Avalonia.Controls
         {
             base.OnApplyTemplate(e);
 
-            _pickerContainer = e.NameScope.Get<Grid>("PickerContainer");
-            _periodHost = e.NameScope.Get<Panel>("PeriodHost");
+            _pickerContainer = e.NameScope.Get<Grid>("PART_PickerContainer");
+            _periodHost = e.NameScope.Get<Panel>("PART_PeriodHost");
 
-            _hourSelector = e.NameScope.Get<DateTimePickerPanel>("HourSelector");
-            _minuteSelector = e.NameScope.Get<DateTimePickerPanel>("MinuteSelector");
-            _periodSelector = e.NameScope.Get<DateTimePickerPanel>("PeriodSelector");
+            _hourSelector = e.NameScope.Get<DateTimePickerPanel>("PART_HourSelector");
+            _minuteSelector = e.NameScope.Get<DateTimePickerPanel>("PART_MinuteSelector");
+            _periodSelector = e.NameScope.Get<DateTimePickerPanel>("PART_PeriodSelector");
 
-            _spacer2 = e.NameScope.Get<Rectangle>("SecondSpacer");
+            _spacer2 = e.NameScope.Get<Rectangle>("PART_SecondSpacer");
 
-            _acceptButton = e.NameScope.Get<Button>("AcceptButton");
+            _acceptButton = e.NameScope.Get<Button>("PART_AcceptButton");
             _acceptButton.Click += OnAcceptButtonClicked;
 
-            _hourUpButton = e.NameScope.Find<RepeatButton>("HourUpButton");
+            _hourUpButton = e.NameScope.Find<RepeatButton>("PART_HourUpButton");
             if (_hourUpButton != null)
                 _hourUpButton.Click += OnSelectorButtonClick;
-            _hourDownButton = e.NameScope.Find<RepeatButton>("HourDownButton");
+            _hourDownButton = e.NameScope.Find<RepeatButton>("PART_HourDownButton");
             if (_hourDownButton != null)
                 _hourDownButton.Click += OnSelectorButtonClick;
 
-            _minuteUpButton = e.NameScope.Find<RepeatButton>("MinuteUpButton");
+            _minuteUpButton = e.NameScope.Find<RepeatButton>("PART_MinuteUpButton");
             if (_minuteUpButton != null)
                 _minuteUpButton.Click += OnSelectorButtonClick;
-            _minuteDownButton = e.NameScope.Find<RepeatButton>("MinuteDownButton");
+            _minuteDownButton = e.NameScope.Find<RepeatButton>("PART_MinuteDownButton");
             if (_minuteDownButton != null)
                 _minuteDownButton.Click += OnSelectorButtonClick;
 
-            _periodUpButton = e.NameScope.Find<RepeatButton>("PeriodUpButton");
+            _periodUpButton = e.NameScope.Find<RepeatButton>("PART_PeriodUpButton");
             if (_periodUpButton != null)
                 _periodUpButton.Click += OnSelectorButtonClick;
-            _periodDownButton = e.NameScope.Find<RepeatButton>("PeriodDownButton");
+            _periodDownButton = e.NameScope.Find<RepeatButton>("PART_PeriodDownButton");
             if (_periodDownButton != null)
                 _periodDownButton.Click += OnSelectorButtonClick;
 
-            _dismissButton = e.NameScope.Find<Button>("DismissButton");
+            _dismissButton = e.NameScope.Find<Button>("PART_DismissButton");
             if (_dismissButton != null)
                 _dismissButton.Click += OnDismissButtonClicked;
 
diff --git a/src/Avalonia.Controls/ToggleSwitch.cs b/src/Avalonia.Controls/ToggleSwitch.cs
index fd6c202c6f..a28e9791f6 100644
--- a/src/Avalonia.Controls/ToggleSwitch.cs
+++ b/src/Avalonia.Controls/ToggleSwitch.cs
@@ -9,8 +9,10 @@ namespace Avalonia.Controls
     /// <summary>
     /// A Toggle Switch control.
     /// </summary>
-    [TemplatePart("MovingKnobs", typeof(Panel))]
-    [TemplatePart("SwitchKnob",  typeof(Panel))]
+    [TemplatePart("PART_MovingKnobs",         typeof(Panel))]
+    [TemplatePart("PART_OffContentPresenter", typeof(ContentPresenter))]
+    [TemplatePart("PART_OnContentPresenter",  typeof(ContentPresenter))]
+    [TemplatePart("PART_SwitchKnob",          typeof(Panel))]
     [PseudoClasses(":dragging")]
     public class ToggleSwitch : ToggleButton
     {
@@ -163,8 +165,8 @@ namespace Avalonia.Controls
         {
             base.OnApplyTemplate(e);
 
-            _switchKnob = e.NameScope.Find<Panel>("SwitchKnob");
-            _knobsPanel = e.NameScope.Get<Panel>("MovingKnobs");
+            _switchKnob = e.NameScope.Find<Panel>("PART_SwitchKnob");
+            _knobsPanel = e.NameScope.Get<Panel>("PART_MovingKnobs");
             
             _knobsPanel.PointerPressed += KnobsPanel_PointerPressed;
             _knobsPanel.PointerReleased += KnobsPanel_PointerReleased;
diff --git a/src/Avalonia.Controls/Utils/BorderRenderHelper.cs b/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
index ecc7cd98bb..eb9f38894d 100644
--- a/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
+++ b/src/Avalonia.Controls/Utils/BorderRenderHelper.cs
@@ -61,7 +61,7 @@ namespace Avalonia.Controls.Utils
                     _backgroundGeometryCache = null;
                 }
 
-                if (boundRect.Width != 0 && innerRect.Height != 0)
+                if (boundRect.Width != 0 && boundRect.Height != 0)
                 {
                     var borderGeometryKeypoints =
                         new BorderGeometryKeypoints(boundRect, borderThickness, cornerRadius, false);
diff --git a/src/Avalonia.Dialogs/ManagedFileChooser.cs b/src/Avalonia.Dialogs/ManagedFileChooser.cs
index ee2ab42d6f..12436680b3 100644
--- a/src/Avalonia.Dialogs/ManagedFileChooser.cs
+++ b/src/Avalonia.Dialogs/ManagedFileChooser.cs
@@ -10,8 +10,8 @@ using Avalonia.LogicalTree;
 
 namespace Avalonia.Dialogs
 {
-    [TemplatePart("QuickLinks", typeof(Control))]
-    [TemplatePart("Files",      typeof(ListBox))]
+    [TemplatePart("PART_QuickLinks", typeof(Control))]
+    [TemplatePart("PART_Files",      typeof(ListBox))]
     public class ManagedFileChooser : TemplatedControl
     {
         private Control _quickLinksRoot;
@@ -90,8 +90,8 @@ namespace Avalonia.Dialogs
 
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
-            _quickLinksRoot = e.NameScope.Get<Control>("QuickLinks");
-            _filesView = e.NameScope.Get<ListBox>("Files");
+            _quickLinksRoot = e.NameScope.Get<Control>("PART_QuickLinks");
+            _filesView = e.NameScope.Get<ListBox>("PART_Files");
         }
     }
 }
diff --git a/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml b/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
index 8d54cb93ca..7042f51c71 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Calendar.xaml
@@ -23,11 +23,11 @@
     <Setter Property="Template">
       <ControlTemplate>
         <StackPanel
-            Name="Root"
+            Name="PART_Root"
             HorizontalAlignment="Center"
             ClipToBounds="True">
           <CalendarItem
-              Name="CalendarItem"
+              Name="PART_CalendarItem"
               Background="{TemplateBinding Background}"
               BorderBrush="{TemplateBinding BorderBrush}"
               BorderThickness="{TemplateBinding BorderThickness}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
index 79c872c640..40ec2c42bb 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
@@ -79,12 +79,12 @@
                  -->
           <Grid VerticalAlignment="Stretch" HorizontalAlignment="Stretch" RowDefinitions="40,*" MinWidth="294">
             <Grid ColumnDefinitions="5*,*,*">
-              <Button Name="HeaderButton"
+              <Button Name="PART_HeaderButton"
                       Theme="{StaticResource FluentCalendarButton}"
                       Foreground="{TemplateBinding Foreground}"
                       Padding="12,0,0,0"
                       HorizontalContentAlignment="Left" />
-              <Button Name="PreviousButton"
+              <Button Name="PART_PreviousButton"
                       Grid.Column="1"
                       Theme="{StaticResource FluentCalendarButton}"
                       Foreground="{TemplateBinding Foreground}"
@@ -97,7 +97,7 @@
                       HorizontalAlignment="Center" 
                       VerticalAlignment="Center" />
               </Button>
-              <Button Name="NextButton"
+              <Button Name="PART_NextButton"
                       Grid.Column="2"
                       Theme="{StaticResource FluentCalendarButton}"
                       Foreground="{TemplateBinding Foreground}"
@@ -113,7 +113,7 @@
             </Grid>
             <!--Border below is used only for MonthView but it can't be moved inside of Grid because CalendarItem expects it to be empty and it will cause side-effects-->
             <Border Name="BackgroundLayer" Background="{TemplateBinding BorderBrush}" Margin="0,38,0,0" IsVisible="{ReflectionBinding #MonthView.IsVisible}" Grid.Row="1" />
-            <Grid Name="MonthView" Grid.Row="1" IsVisible="False" MinHeight="290">
+            <Grid Name="PART_MonthView" Grid.Row="1" IsVisible="False" MinHeight="290">
               <Grid.RowDefinitions>
                 <!--This should always be the week day names??-->
                 <RowDefinition Height="38" />
@@ -134,7 +134,7 @@
                 <ColumnDefinition Width="Auto" />
               </Grid.ColumnDefinitions>
             </Grid>
-            <Grid Name="YearView"
+            <Grid Name="PART_YearView"
                   Background="{TemplateBinding BorderBrush}"
                   MinHeight="290"
                   Grid.Row="1"
diff --git a/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
index e9c60570c7..0cfd491b21 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml
@@ -94,7 +94,7 @@
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Top"/>
 
-            <Button Name="FlyoutButton"
+            <Button Name="PART_FlyoutButton"
                     Grid.Row="1"
                     Theme="{StaticResource FluentDatePickerFlyoutButton}"
                     Foreground="{TemplateBinding Foreground}"
@@ -108,28 +108,28 @@
                     HorizontalAlignment="Stretch"
                     VerticalAlignment="Stretch"
                     TemplatedControl.IsTemplateFocusTarget="True">
-              <Grid Name="ButtonContentGrid" ColumnDefinitions="78*,Auto,132*,Auto,78*">
-                <TextBlock Name="DayText" Text="day" HorizontalAlignment="Center"
+              <Grid Name="PART_ButtonContentGrid" ColumnDefinitions="78*,Auto,132*,Auto,78*">
+                <TextBlock Name="PART_DayTextBlock" Text="day" HorizontalAlignment="Center"
                            Padding="{DynamicResource DatePickerHostPadding}"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontWeight="{TemplateBinding FontWeight}"
                            FontSize="{TemplateBinding FontSize}"/>
-                <TextBlock Name="MonthText" Text="month" TextAlignment="Left"
+                <TextBlock Name="PART_MonthTextBlock" Text="month" TextAlignment="Left"
                            Padding="{DynamicResource DatePickerHostMonthPadding}"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontWeight="{TemplateBinding FontWeight}"
                            FontSize="{TemplateBinding FontSize}"/>
-                <TextBlock Name="YearText" Text="year" HorizontalAlignment="Center"
+                <TextBlock Name="PART_YearTextBlock" Text="year" HorizontalAlignment="Center"
                            Padding="{DynamicResource DatePickerHostPadding}"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontWeight="{TemplateBinding FontWeight}"
                            FontSize="{TemplateBinding FontSize}"/>
-                <Rectangle x:Name="FirstSpacer"
+                <Rectangle x:Name="PART_FirstSpacer"
                       Fill="{DynamicResource DatePickerSpacerFill}"
                       HorizontalAlignment="Center"
                       Width="1"
                       Grid.Column="1" />
-                <Rectangle x:Name="SecondSpacer"
+                <Rectangle x:Name="PART_SecondSpacer"
                       Fill="{DynamicResource DatePickerSpacerFill}"
                       HorizontalAlignment="Center"
                       Width="1"
@@ -137,10 +137,10 @@
               </Grid>
             </Button>
 
-            <Popup Name="Popup" WindowManagerAddShadowHint="False"
+            <Popup Name="PART_Popup" WindowManagerAddShadowHint="False"
                    IsLightDismissEnabled="True" PlacementTarget="{TemplateBinding}"
                    PlacementMode="Bottom">
-              <DatePickerPresenter Name="PickerPresenter" />
+              <DatePickerPresenter Name="PART_PickerPresenter" />
             </Popup>
 
           </Grid>
@@ -181,62 +181,62 @@
                 Padding="{DynamicResource DateTimeFlyoutBorderPadding}"
                 MaxHeight="398" CornerRadius="{TemplateBinding CornerRadius}">
           <Grid Name="ContentRoot" RowDefinitions="*,Auto">
-            <Grid Name="PickerContainer">
+            <Grid Name="PART_PickerContainer">
               <Grid.Styles>
                 <Style Selector="DateTimePickerPanel > ListBoxItem">
                   <Setter Property="Theme" Value="{StaticResource FluentDateTimePickerItem}" />
                 </Style>
               </Grid.Styles>
               <!--Column Definitions set in code, ignore here-->
-              <Panel Name="MonthHost">
+              <Panel Name="PART_MonthHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="MonthSelector"
+                  <DateTimePickerPanel Name="PART_MonthSelector"
                                        PanelType="Month"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="MonthUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="MonthDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_MonthUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_MonthDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
-              <Panel Name="DayHost">
+              <Panel Name="PART_DayHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="DaySelector"
+                  <DateTimePickerPanel Name="PART_DaySelector"
                                        PanelType="Day"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="DayUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="DayDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_DayUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_DayDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
-              <Panel Name="YearHost">
+              <Panel Name="PART_YearHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="YearSelector"
+                  <DateTimePickerPanel Name="PART_YearSelector"
                                        PanelType="Year"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        ShouldLoop="False" />
                 </ScrollViewer>
-                <RepeatButton Name="YearUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="YearDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_YearUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_YearDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
               <Rectangle Name="HighlightRect" IsHitTestVisible="False" ZIndex="-1"
                          Fill="{DynamicResource DatePickerFlyoutPresenterHighlightFill}"
                          Grid.Column="0" Grid.ColumnSpan="5" VerticalAlignment="Center"
                          Height="{DynamicResource DatePickerFlyoutPresenterHighlightHeight}" />
-              <Rectangle Name="FirstSpacer"
+              <Rectangle Name="PART_FirstSpacer"
                          Fill="{DynamicResource DatePickerFlyoutPresenterSpacerFill}"
                          HorizontalAlignment="Center"
                          Width="{DynamicResource DatePickerSpacerThemeWidth}"
                          Grid.Column="1" />
-              <Rectangle Name="SecondSpacer"
+              <Rectangle Name="PART_SecondSpacer"
                          Fill="{DynamicResource DatePickerFlyoutPresenterSpacerFill}"
                          HorizontalAlignment="Center"
                          Width="{DynamicResource DatePickerSpacerThemeWidth}"
                          Grid.Column="3" />
             </Grid>
-            
+
             <Grid Name="AcceptDismissGrid"
                   Grid.Row="1"
                   ColumnDefinitions="*,*">
@@ -244,7 +244,7 @@
                          VerticalAlignment="Top"
                          Fill="{DynamicResource DatePickerFlyoutPresenterSpacerFill}"
                          Grid.ColumnSpan="2"/>
-              <Button Name="AcceptButton"
+              <Button Name="PART_AcceptButton"
                       Grid.Column="0"
                       Theme="{StaticResource FluentDateTimePickerButton}"
                       Height="{DynamicResource DatePickerFlyoutPresenterAcceptDismissHostGridHeight}"
@@ -255,8 +255,8 @@
                       StrokeThickness="0.75"
                       Data="M0.5,8.5 5,13.5 15.5,3" />
               </Button>
-              <Button Name="DismissButton" 
-                      Grid.Column="1" 
+              <Button Name="PART_DismissButton"
+                      Grid.Column="1"
                       Theme="{StaticResource FluentDateTimePickerButton}"
                       Height="{DynamicResource DatePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       HorizontalAlignment="Stretch" 
diff --git a/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml b/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
index b8ade96b6f..d0280b16a2 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ManagedFileChooser.xaml
@@ -134,7 +134,7 @@
     <Setter Property="Template">
       <ControlTemplate>
         <DockPanel>
-          <ListBox x:Name="QuickLinks" DockPanel.Dock="Left" Items="{Binding QuickLinks}" SelectedIndex="{Binding QuickLinksSelectedIndex}" Focusable="False">
+          <ListBox x:Name="PART_QuickLinks" DockPanel.Dock="Left" Items="{Binding QuickLinks}" SelectedIndex="{Binding QuickLinksSelectedIndex}" Focusable="False">
             <ListBox.ItemTemplate>
               <DataTemplate>
                 <StackPanel Spacing="4" Orientation="Horizontal" Background="Transparent">
@@ -213,7 +213,7 @@
               <GridSplitter Grid.Column="7" />
               <TextBlock Grid.Column="8" Text="Size" />
             </Grid>
-            <ListBox x:Name="Files"
+            <ListBox x:Name="PART_Files"
                 VirtualizationMode="Simple"
                 Items="{Binding Items}"
                 Margin="0 5"
diff --git a/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
index fb02071c3f..fcd661a4b5 100644
--- a/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/TimePicker.xaml
@@ -94,7 +94,7 @@
                               HorizontalAlignment="Stretch"
                               VerticalAlignment="Top" />
 
-            <Button x:Name="FlyoutButton"
+            <Button x:Name="PART_FlyoutButton"
                     Grid.Row="1"
                     Theme="{StaticResource FluentTimePickerFlyoutButton}"
                     Foreground="{TemplateBinding Foreground}"
@@ -108,13 +108,13 @@
                     HorizontalAlignment="Stretch"
                     VerticalAlignment="Top">
 
-              <Grid Name="FlyoutButtonContentGrid">
+              <Grid Name="PART_FlyoutButtonContentGrid">
                 <!--Ignore col defs here, set in code-->
-                <Border x:Name="FirstPickerHost"
+                <Border x:Name="PART_FirstPickerHost"
                         Grid.Column="0"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="HourTextBlock"
+                  <TextBlock x:Name="PART_HourTextBlock"
                       HorizontalAlignment="Center"
                       Padding="{DynamicResource TimePickerHostPadding}"
                       FontFamily="{TemplateBinding FontFamily}"
@@ -122,17 +122,17 @@
                       FontSize="{TemplateBinding FontSize}" />
                 </Border>
 
-                <Rectangle Name="FirstColumnDivider"
+                <Rectangle Name="PART_FirstColumnDivider"
                            Fill="{DynamicResource TimePickerSpacerFill}"
                            HorizontalAlignment="Center"
                            Width="{DynamicResource TimePickerSpacerThemeWidth}"
                            Grid.Column="1" />
 
-                <Border x:Name="SecondPickerHost"
+                <Border x:Name="PART_SecondPickerHost"
                         Grid.Column="2"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="MinuteTextBlock"
+                  <TextBlock x:Name="PART_MinuteTextBlock"
                              HorizontalAlignment="Center"
                              Padding="{DynamicResource TimePickerHostPadding}"
                              FontFamily="{TemplateBinding FontFamily}"
@@ -140,17 +140,17 @@
                              FontSize="{TemplateBinding FontSize}"/>
                 </Border>
 
-                <Rectangle Name="SecondColumnDivider"
+                <Rectangle Name="PART_SecondColumnDivider"
                            Fill="{DynamicResource TimePickerSpacerFill}"
                            HorizontalAlignment="Center"
                            Width="{DynamicResource TimePickerSpacerThemeWidth}"
                            Grid.Column="3" />
 
-                <Border x:Name="ThirdPickerHost"
+                <Border x:Name="PART_ThirdPickerHost"
                         Grid.Column="4"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="PeriodTextBlock"
+                  <TextBlock x:Name="PART_PeriodTextBlock"
                              HorizontalAlignment="Center"
                              Padding="{DynamicResource TimePickerHostPadding}"
                              FontFamily="{TemplateBinding FontFamily}"
@@ -160,12 +160,12 @@
               </Grid>
             </Button>
 
-            <Popup Name="Popup"
+            <Popup Name="PART_Popup"
                    WindowManagerAddShadowHint="False"
                    IsLightDismissEnabled="True"
                    PlacementTarget="{TemplateBinding}"
                    PlacementMode="Bottom">
-              <TimePickerPresenter Name="PickerPresenter" />
+              <TimePickerPresenter Name="PART_PickerPresenter" />
             </Popup>
 
           </Grid>
@@ -209,42 +209,42 @@
                 Padding="{DynamicResource DateTimeFlyoutBorderPadding}"
                 MaxHeight="398">
           <Grid Name="ContentPanel" RowDefinitions="*,Auto">
-            <Grid Name="PickerContainer">
+            <Grid Name="PART_PickerContainer">
               <!--Ignore col defs here, set in code-->
-              <Panel Name="HourHost" Grid.Column="0">
+              <Panel Name="PART_HourHost" Grid.Column="0">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="HourSelector"
+                  <DateTimePickerPanel Name="PART_HourSelector"
                                        PanelType="Hour"
                                        ShouldLoop="True"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"/>
                 </ScrollViewer>
-                <RepeatButton Name="HourUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="HourDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_HourUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_HourDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
 
-              <Panel Name="MinuteHost" Grid.Column="2">
+              <Panel Name="PART_MinuteHost" Grid.Column="2">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="MinuteSelector"
+                  <DateTimePickerPanel Name="PART_MinuteSelector"
                                        PanelType="Minute"
                                        ShouldLoop="True"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"/>
                 </ScrollViewer>
-                <RepeatButton Name="MinuteUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="MinuteDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_MinuteUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_MinuteDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
 
-              <Panel Name="PeriodHost" Grid.Column="4">
+              <Panel Name="PART_PeriodHost" Grid.Column="4">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="PeriodSelector"
+                  <DateTimePickerPanel Name="PART_PeriodSelector"
                                        PanelType="TimePeriod"
                                        ShouldLoop="False"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"/>
                 </ScrollViewer>
-                <RepeatButton Name="PeriodUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
-                <RepeatButton Name="PeriodDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
+                <RepeatButton Name="PART_PeriodUpButton" Theme="{StaticResource FluentDateTimePickerUpButton}"/>
+                <RepeatButton Name="PART_PeriodDownButton" Theme="{StaticResource FluentDateTimePickerDownButton}"/>
               </Panel>
 
               <Rectangle x:Name="HighlightRect" ZIndex="-1"
@@ -253,12 +253,12 @@
                          Grid.ColumnSpan="5"
                          VerticalAlignment="Center"
                          Height="{DynamicResource TimePickerFlyoutPresenterHighlightHeight}" />
-              <Rectangle Name="FirstSpacer"
+              <Rectangle Name="PART_FirstSpacer"
                          Fill="{DynamicResource TimePickerFlyoutPresenterSpacerFill}"
                          HorizontalAlignment="Center"
                          Width="{DynamicResource TimePickerSpacerThemeWidth}"
                          Grid.Column="1" />
-              <Rectangle Name="SecondSpacer"
+              <Rectangle Name="PART_SecondSpacer"
                          Fill="{DynamicResource TimePickerFlyoutPresenterSpacerFill}"
                          HorizontalAlignment="Center"
                          Width="{DynamicResource TimePickerSpacerThemeWidth}"
@@ -272,7 +272,7 @@
                          VerticalAlignment="Top"
                          Fill="{DynamicResource TimePickerFlyoutPresenterSpacerFill}"
                          Grid.ColumnSpan="2"/>
-              <Button Name="AcceptButton"
+              <Button Name="PART_AcceptButton"
                       Grid.Column="0"
                       Theme="{StaticResource FluentDateTimePickerButton}"
                       Height="{DynamicResource TimePickerFlyoutPresenterAcceptDismissHostGridHeight}"
@@ -283,8 +283,8 @@
                       StrokeThickness="0.75"
                       Data="M0.5,8.5 5,13.5 15.5,3" />
               </Button>
-              <Button Name="DismissButton" 
-                      Grid.Column="1" 
+              <Button Name="PART_DismissButton"
+                      Grid.Column="1"
                       Theme="{StaticResource FluentDateTimePickerButton}"
                       Height="{DynamicResource TimePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       FontSize="16" 
diff --git a/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml b/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
index aaa20a105c..1ba8c237ee 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ToggleSwitch.xaml
@@ -106,13 +106,13 @@
                 CornerRadius="10" />
 
             <Canvas
-                x:Name="SwitchKnob"
+                x:Name="PART_SwitchKnob"
                 Grid.Row="1"
                 Width="20"
                 Height="20"
                 HorizontalAlignment="Left">
 
-              <Grid x:Name="MovingKnobs" Width="20" Height="20">
+              <Grid x:Name="PART_MovingKnobs" Width="20" Height="20">
                 <Ellipse
                   x:Name="SwitchKnobOn"
                   Fill="{DynamicResource ToggleSwitchKnobFillOn}"
diff --git a/src/Avalonia.Themes.Simple/Controls/Calendar.xaml b/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
index 6f7267581b..08305319e1 100644
--- a/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/Calendar.xaml
@@ -16,10 +16,10 @@
     <Setter Property="HeaderBackground" Value="{DynamicResource ThemeAccentBrush2}" />
     <Setter Property="Template">
       <ControlTemplate>
-        <StackPanel Name="Root"
+        <StackPanel Name="PART_Root"
                     HorizontalAlignment="Center"
                     ClipToBounds="True">
-          <CalendarItem Name="CalendarItem"
+          <CalendarItem Name="PART_CalendarItem"
                         Background="{TemplateBinding Background}"
                         BorderBrush="{TemplateBinding BorderBrush}"
                         BorderThickness="{TemplateBinding BorderThickness}"
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
index e06034fe09..d9acd0d25a 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarItem.xaml
@@ -65,7 +65,7 @@
                            Fill="{TemplateBinding HeaderBackground}"
                            Stretch="Fill" />
 
-                <Button Name="PreviousButton"
+                <Button Name="PART_PreviousButton"
                         HorizontalAlignment="Left"
                         Classes="CalendarHeader CalendarNavigation"
                         IsVisible="False">
@@ -80,7 +80,7 @@
 
                 </Button>
 
-                <Button Name="HeaderButton"
+                <Button Name="PART_HeaderButton"
                         Grid.Column="1"
                         Padding="1,5,1,9"
                         HorizontalAlignment="Center"
@@ -89,7 +89,7 @@
                         FontSize="10.5"
                         FontWeight="Bold" />
 
-                <Button Name="NextButton"
+                <Button Name="PART_NextButton"
                         Grid.Column="2"
                         HorizontalAlignment="Right"
                         Classes="CalendarHeader CalendarNavigation"
@@ -105,7 +105,7 @@
 
                 </Button>
 
-                <Grid Name="MonthView"
+                <Grid Name="PART_MonthView"
                       Grid.Row="1"
                       Grid.ColumnSpan="3"
                       Margin="6,-1,6,6"
@@ -130,7 +130,7 @@
                   </Grid.ColumnDefinitions>
                 </Grid>
 
-                <Grid Name="YearView"
+                <Grid Name="PART_YearView"
                       Grid.Row="1"
                       Grid.ColumnSpan="3"
                       Margin="6,-3,7,6"
diff --git a/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml b/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
index a6da2ad9f8..317a27435a 100644
--- a/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DatePicker.xaml
@@ -102,7 +102,7 @@
                               Content="{TemplateBinding Header}"
                               ContentTemplate="{TemplateBinding HeaderTemplate}" />
 
-            <Button Name="FlyoutButton"
+            <Button Name="PART_FlyoutButton"
                     Grid.Row="1"
                     MinWidth="{DynamicResource DatePickerThemeMinWidth}"
                     MaxWidth="{DynamicResource DatePickerThemeMaxWidth}"
@@ -116,35 +116,35 @@
                     IsEnabled="{TemplateBinding IsEnabled}"
                     TemplatedControl.IsTemplateFocusTarget="True"
                     Theme="{StaticResource SimpleDatePickerFlyoutButton}">
-              <Grid Name="ButtonContentGrid"
+              <Grid Name="PART_ButtonContentGrid"
                     ColumnDefinitions="78*,Auto,132*,Auto,78*">
-                <TextBlock Name="DayText"
+                <TextBlock Name="PART_DayTextBlock"
                            Padding="{DynamicResource DatePickerHostPadding}"
                            HorizontalAlignment="Center"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontSize="{TemplateBinding FontSize}"
                            FontWeight="{TemplateBinding FontWeight}"
                            Text="day" />
-                <TextBlock Name="MonthText"
+                <TextBlock Name="PART_MonthTextBlock"
                            Padding="{DynamicResource DatePickerHostMonthPadding}"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontSize="{TemplateBinding FontSize}"
                            FontWeight="{TemplateBinding FontWeight}"
                            Text="month"
                            TextAlignment="Left" />
-                <TextBlock Name="YearText"
+                <TextBlock Name="PART_YearTextBlock"
                            Padding="{DynamicResource DatePickerHostPadding}"
                            HorizontalAlignment="Center"
                            FontFamily="{TemplateBinding FontFamily}"
                            FontSize="{TemplateBinding FontSize}"
                            FontWeight="{TemplateBinding FontWeight}"
                            Text="year" />
-                <Rectangle x:Name="FirstSpacer"
+                <Rectangle x:Name="PART_FirstSpacer"
                            Grid.Column="1"
                            Width="1"
                            HorizontalAlignment="Center"
                            Fill="{DynamicResource DatePickerSpacerFill}" />
-                <Rectangle x:Name="SecondSpacer"
+                <Rectangle x:Name="PART_SecondSpacer"
                            Grid.Column="3"
                            Width="1"
                            HorizontalAlignment="Center"
@@ -152,12 +152,12 @@
               </Grid>
             </Button>
 
-            <Popup Name="Popup"
+            <Popup Name="PART_Popup"
                    IsLightDismissEnabled="True"
                    PlacementMode="Bottom"
                    PlacementTarget="{TemplateBinding}"
                    WindowManagerAddShadowHint="False">
-              <DatePickerPresenter Name="PickerPresenter" />
+              <DatePickerPresenter Name="PART_PickerPresenter" />
             </Popup>
 
           </Grid>
@@ -197,50 +197,50 @@
                 CornerRadius="{TemplateBinding CornerRadius}">
           <Grid Name="ContentRoot"
                 RowDefinitions="*,Auto">
-            <Grid Name="PickerContainer">
+            <Grid Name="PART_PickerContainer">
               <Grid.Styles>
                 <Style Selector="DateTimePickerPanel > ListBoxItem">
                   <Setter Property="Theme" Value="{StaticResource SimpleDateTimePickerItem}" />
                 </Style>
               </Grid.Styles>
               <!--  Column Definitions set in code, ignore here  -->
-              <Panel Name="MonthHost">
+              <Panel Name="PART_MonthHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="MonthSelector"
+                  <DateTimePickerPanel Name="PART_MonthSelector"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        PanelType="Month"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="MonthUpButton"
+                <RepeatButton Name="PART_MonthUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="MonthDownButton"
+                <RepeatButton Name="PART_MonthDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
-              <Panel Name="DayHost">
+              <Panel Name="PART_DayHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="DaySelector"
+                  <DateTimePickerPanel Name="PART_DaySelector"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        PanelType="Day"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="DayUpButton"
+                <RepeatButton Name="PART_DayUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="DayDownButton"
+                <RepeatButton Name="PART_DayDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
-              <Panel Name="YearHost">
+              <Panel Name="PART_YearHost">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="YearSelector"
+                  <DateTimePickerPanel Name="PART_YearSelector"
                                        ItemHeight="{DynamicResource DatePickerFlyoutPresenterItemHeight}"
                                        PanelType="Year"
                                        ShouldLoop="False" />
                 </ScrollViewer>
-                <RepeatButton Name="YearUpButton"
+                <RepeatButton Name="PART_YearUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="YearDownButton"
+                <RepeatButton Name="PART_YearDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
               <Rectangle Name="HighlightRect"
@@ -255,12 +255,12 @@
                                    Color="{DynamicResource ThemeAccentColor}" />
                 </Rectangle.Fill>
               </Rectangle>
-              <Rectangle Name="FirstSpacer"
+              <Rectangle Name="PART_FirstSpacer"
                          Grid.Column="1"
                          Width="{DynamicResource DatePickerSpacerThemeWidth}"
                          HorizontalAlignment="Center"
                          Fill="{DynamicResource ThemeControlMidHighBrush}" />
-              <Rectangle Name="SecondSpacer"
+              <Rectangle Name="PART_SecondSpacer"
                          Grid.Column="3"
                          Width="{DynamicResource DatePickerSpacerThemeWidth}"
                          HorizontalAlignment="Center"
@@ -274,7 +274,7 @@
                          Height="{DynamicResource DatePickerSpacerThemeWidth}"
                          VerticalAlignment="Top"
                          Fill="{DynamicResource ThemeControlMidHighBrush}" />
-              <Button Name="AcceptButton"
+              <Button Name="PART_AcceptButton"
                       Grid.Column="0"
                       Height="{DynamicResource DatePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       HorizontalAlignment="Stretch"
@@ -285,7 +285,7 @@
                       StrokeLineCap="Round"
                       StrokeThickness="0.75" />
               </Button>
-              <Button Name="DismissButton"
+              <Button Name="PART_DismissButton"
                       Grid.Column="1"
                       Height="{DynamicResource DatePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       HorizontalAlignment="Stretch"
diff --git a/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml b/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
index 52d9000396..3416b5406e 100644
--- a/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ManagedFileChooser.xaml
@@ -94,7 +94,7 @@
                    Text="{Binding FileName}"
                    Watermark="File name" />
 
-          <ListBox x:Name="QuickLinks"
+          <ListBox x:Name="PART_QuickLinks"
                    Margin="0,0,5,5"
                    BorderBrush="Transparent"
                    DockPanel.Dock="Left"
@@ -143,7 +143,7 @@
               <TextBlock Grid.Column="8"
                          Text="Size" />
             </Grid>
-            <ListBox x:Name="Files"
+            <ListBox x:Name="PART_Files"
                      Margin="0,5"
                      Items="{Binding Items}"
                      ScrollViewer.HorizontalScrollBarVisibility="Disabled"
diff --git a/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml b/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
index c49b3aec4e..5aa717e9ee 100644
--- a/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/TimePicker.xaml
@@ -102,7 +102,7 @@
                               ContentTemplate="{TemplateBinding HeaderTemplate}"
                               Foreground="{DynamicResource ThemeForegroundColor}" />
 
-            <Button x:Name="FlyoutButton"
+            <Button x:Name="PART_FlyoutButton"
                     Grid.Row="1"
                     MinWidth="{DynamicResource TimePickerThemeMinWidth}"
                     MaxWidth="{DynamicResource TimePickerThemeMaxWidth}"
@@ -116,13 +116,13 @@
                     IsEnabled="{TemplateBinding IsEnabled}"
                     Theme="{StaticResource SimpleTimePickerFlyoutButton}">
 
-              <Grid Name="FlyoutButtonContentGrid">
+              <Grid Name="PART_FlyoutButtonContentGrid">
                 <!--  Ignore col defs here, set in code  -->
-                <Border x:Name="FirstPickerHost"
+                <Border x:Name="PART_FirstPickerHost"
                         Grid.Column="0"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="HourTextBlock"
+                  <TextBlock x:Name="PART_HourTextBlock"
                              Padding="{DynamicResource TimePickerHostPadding}"
                              HorizontalAlignment="Center"
                              FontFamily="{TemplateBinding FontFamily}"
@@ -130,17 +130,17 @@
                              FontWeight="{TemplateBinding FontWeight}" />
                 </Border>
 
-                <Rectangle Name="FirstColumnDivider"
+                <Rectangle Name="PART_FirstColumnDivider"
                            Grid.Column="1"
                            Width="{DynamicResource TimePickerSpacerThemeWidth}"
                            HorizontalAlignment="Center"
                            Fill="{DynamicResource TimePickerSpacerFill}" />
 
-                <Border x:Name="SecondPickerHost"
+                <Border x:Name="PART_SecondPickerHost"
                         Grid.Column="2"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="MinuteTextBlock"
+                  <TextBlock x:Name="PART_MinuteTextBlock"
                              Padding="{DynamicResource TimePickerHostPadding}"
                              HorizontalAlignment="Center"
                              FontFamily="{TemplateBinding FontFamily}"
@@ -148,17 +148,17 @@
                              FontWeight="{TemplateBinding FontWeight}" />
                 </Border>
 
-                <Rectangle Name="SecondColumnDivider"
+                <Rectangle Name="PART_SecondColumnDivider"
                            Grid.Column="3"
                            Width="{DynamicResource TimePickerSpacerThemeWidth}"
                            HorizontalAlignment="Center"
                            Fill="{DynamicResource TimePickerSpacerFill}" />
 
-                <Border x:Name="ThirdPickerHost"
+                <Border x:Name="PART_ThirdPickerHost"
                         Grid.Column="4"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Stretch">
-                  <TextBlock x:Name="PeriodTextBlock"
+                  <TextBlock x:Name="PART_PeriodTextBlock"
                              Padding="{DynamicResource TimePickerHostPadding}"
                              HorizontalAlignment="Center"
                              FontFamily="{TemplateBinding FontFamily}"
@@ -168,12 +168,12 @@
               </Grid>
             </Button>
 
-            <Popup Name="Popup"
+            <Popup Name="PART_Popup"
                    IsLightDismissEnabled="True"
                    PlacementMode="Bottom"
                    PlacementTarget="{TemplateBinding}"
                    WindowManagerAddShadowHint="False">
-              <TimePickerPresenter Name="PickerPresenter" />
+              <TimePickerPresenter Name="PART_PickerPresenter" />
             </Popup>
 
           </Grid>
@@ -214,50 +214,50 @@
                 CornerRadius="{TemplateBinding CornerRadius}">
           <Grid Name="ContentPanel"
                 RowDefinitions="*,Auto">
-            <Grid Name="PickerContainer">
+            <Grid Name="PART_PickerContainer">
               <!--  Ignore col defs here, set in code  -->
-              <Panel Name="HourHost"
+              <Panel Name="PART_HourHost"
                      Grid.Column="0">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="HourSelector"
+                  <DateTimePickerPanel Name="PART_HourSelector"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"
                                        PanelType="Hour"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="HourUpButton"
+                <RepeatButton Name="PART_HourUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="HourDownButton"
+                <RepeatButton Name="PART_HourDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
 
-              <Panel Name="MinuteHost"
+              <Panel Name="PART_MinuteHost"
                      Grid.Column="2">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="MinuteSelector"
+                  <DateTimePickerPanel Name="PART_MinuteSelector"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"
                                        PanelType="Minute"
                                        ShouldLoop="True" />
                 </ScrollViewer>
-                <RepeatButton Name="MinuteUpButton"
+                <RepeatButton Name="PART_MinuteUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="MinuteDownButton"
+                <RepeatButton Name="PART_MinuteDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
 
-              <Panel Name="PeriodHost"
+              <Panel Name="PART_PeriodHost"
                      Grid.Column="4">
                 <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                               VerticalScrollBarVisibility="Hidden">
-                  <DateTimePickerPanel Name="PeriodSelector"
+                  <DateTimePickerPanel Name="PART_PeriodSelector"
                                        ItemHeight="{DynamicResource TimePickerFlyoutPresenterItemHeight}"
                                        PanelType="TimePeriod"
                                        ShouldLoop="False" />
                 </ScrollViewer>
-                <RepeatButton Name="PeriodUpButton"
+                <RepeatButton Name="PART_PeriodUpButton"
                               Theme="{StaticResource SimpleDateTimePickerUpButton}" />
-                <RepeatButton Name="PeriodDownButton"
+                <RepeatButton Name="PART_PeriodDownButton"
                               Theme="{StaticResource SimpleDateTimePickerDownButton}" />
               </Panel>
 
@@ -272,12 +272,12 @@
                                    Color="{DynamicResource ThemeAccentColor}" />
                 </Rectangle.Fill>
               </Rectangle>
-              <Rectangle Name="FirstSpacer"
+              <Rectangle Name="PART_FirstSpacer"
                          Grid.Column="1"
                          Width="{DynamicResource TimePickerSpacerThemeWidth}"
                          HorizontalAlignment="Center"
                          Fill="{DynamicResource ThemeControlMidHighBrush}" />
-              <Rectangle Name="SecondSpacer"
+              <Rectangle Name="PART_SecondSpacer"
                          Grid.Column="3"
                          Width="{DynamicResource TimePickerSpacerThemeWidth}"
                          HorizontalAlignment="Center"
@@ -291,7 +291,7 @@
                          Height="{DynamicResource TimePickerSpacerThemeWidth}"
                          VerticalAlignment="Top"
                          Fill="{DynamicResource ThemeControlMidHighBrush}" />
-              <Button Name="AcceptButton"
+              <Button Name="PART_AcceptButton"
                       Grid.Column="0"
                       Height="{DynamicResource TimePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       HorizontalAlignment="Stretch"
@@ -302,7 +302,7 @@
                       StrokeLineCap="Round"
                       StrokeThickness="0.75" />
               </Button>
-              <Button Name="DismissButton"
+              <Button Name="PART_DismissButton"
                       Grid.Column="1"
                       Height="{DynamicResource TimePickerFlyoutPresenterAcceptDismissHostGridHeight}"
                       HorizontalAlignment="Stretch"
diff --git a/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml b/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
index d00358951a..0815f487f8 100644
--- a/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/ToggleSwitch.xaml
@@ -149,11 +149,11 @@
                     BorderBrush="{DynamicResource ToggleSwitchStrokeOn}"
                     BorderThickness="{DynamicResource ToggleSwitchOnStrokeThickness}" />
 
-            <Canvas x:Name="SwitchKnob" Grid.Row="1"
+            <Canvas x:Name="PART_SwitchKnob" Grid.Row="1"
                     HorizontalAlignment="Left"
                     Width="20" Height="20">
 
-              <Grid x:Name="MovingKnobs"
+              <Grid x:Name="PART_MovingKnobs"
                     Width="20" Height="20">
                 <Grid.Transitions>
                   <Transitions>
diff --git a/src/tools/DevAnalyzers/OnPropertyChangedOverrideAnalyzer.cs b/src/tools/DevAnalyzers/OnPropertyChangedOverrideAnalyzer.cs
new file mode 100644
index 0000000000..a16542fdc0
--- /dev/null
+++ b/src/tools/DevAnalyzers/OnPropertyChangedOverrideAnalyzer.cs
@@ -0,0 +1,64 @@
+using System.Collections.Immutable;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace DevAnalyzers
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class OnPropertyChangedOverrideAnalyzer : DiagnosticAnalyzer
+    {
+        public const string DiagnosticId = "AVADEV2001";
+
+        private static readonly DiagnosticDescriptor Rule = new DiagnosticDescriptor(
+            DiagnosticId,
+            "Missing invoke base.OnPropertyChanged",
+            "Method '{0}' do not invoke base.{0}",
+            "Potential issue",
+            DiagnosticSeverity.Warning,
+            isEnabledByDefault: true,
+            description: "The OnPropertyChanged of the base class was not invoked in the override method declaration, which could lead to unwanted behavior.");
+
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.EnableConcurrentExecution();
+            context.RegisterSymbolAction(AnalyzeMethod, SymbolKind.Method);
+        }
+
+        private static void AnalyzeMethod(SymbolAnalysisContext context)
+        {
+            if (context.Symbol is IMethodSymbol currentMethod
+                && currentMethod.Name == "OnPropertyChanged"
+                && currentMethod.OverriddenMethod is IMethodSymbol originalMethod)
+            {
+                var declaration = currentMethod.DeclaringSyntaxReferences.FirstOrDefault()
+                    ?.GetSyntax(context.CancellationToken);
+                if (declaration is not null && context.Compilation.GetSemanticModel(declaration!.SyntaxTree) is { } semanticModel)
+                {
+                    if (declaration.SyntaxTree.TryGetRoot(out var root))
+                    {
+                        var baseInvocations = root.DescendantNodes().OfType<BaseExpressionSyntax>();
+                        if (baseInvocations.Any())
+                        {
+                            foreach (var baseInvocation in baseInvocations)
+                            {
+                                var parent = baseInvocation.Parent;
+                                var targetSymbol = semanticModel.GetSymbolInfo(parent, context.CancellationToken);
+                                if (SymbolEqualityComparer.Default.Equals(targetSymbol.Symbol, originalMethod))
+                                {
+                                    return;
+                                }
+                            }
+                        }
+                        context.ReportDiagnostic(Diagnostic.Create(Rule, currentMethod.Locations[0], currentMethod.Name));
+                    }
+                }
+            }
+        }
+
+    }
+}
diff --git a/src/tools/DevGenerators/CompositionGenerator/CompositionRoslynGenerator.cs b/src/tools/DevGenerators/CompositionGenerator/CompositionRoslynGenerator.cs
index 72311b4d18..26bd4796df 100644
--- a/src/tools/DevGenerators/CompositionGenerator/CompositionRoslynGenerator.cs
+++ b/src/tools/DevGenerators/CompositionGenerator/CompositionRoslynGenerator.cs
@@ -11,8 +11,9 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
         {
             var schema =
                 context.AdditionalTextsProvider.Where(static file => file.Path.EndsWith("composition-schema.xml"));
-            var configs = schema.Select((t, _) =>
-                (GConfig)new XmlSerializer(typeof(GConfig)).Deserialize(new StringReader(t.GetText().ToString())));
+            var configs = schema.Select((t, _) => t.GetText())
+                .Where(source => source is not null)
+                .Select((source, _) => (GConfig)new XmlSerializer(typeof(GConfig)).Deserialize(new StringReader(source!.ToString())));
             context.RegisterSourceOutput(configs, (spc, config) =>
             {
                 var generator = new Generator(new RoslynCompositionGeneratorSink(spc), config);
@@ -20,4 +21,4 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             });
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/tools/DevGenerators/CompositionGenerator/Extensions.cs b/src/tools/DevGenerators/CompositionGenerator/Extensions.cs
index d88e9b4600..f34765ec36 100644
--- a/src/tools/DevGenerators/CompositionGenerator/Extensions.cs
+++ b/src/tools/DevGenerators/CompositionGenerator/Extensions.cs
@@ -7,49 +7,47 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
 {
     public static class Extensions
     {
-        public static ClassDeclarationSyntax AddModifiers(this ClassDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static ClassDeclarationSyntax AddModifiers(this ClassDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
         
-        public static MethodDeclarationSyntax AddModifiers(this MethodDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static MethodDeclarationSyntax AddModifiers(this MethodDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
         
-        public static PropertyDeclarationSyntax AddModifiers(this PropertyDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static PropertyDeclarationSyntax AddModifiers(this PropertyDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
 
-        public static ConstructorDeclarationSyntax AddModifiers(this ConstructorDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static ConstructorDeclarationSyntax AddModifiers(this ConstructorDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
         
-        public static AccessorDeclarationSyntax AddModifiers(this AccessorDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static AccessorDeclarationSyntax AddModifiers(this AccessorDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
         
-        public static EnumDeclarationSyntax AddModifiers(this EnumDeclarationSyntax cl, params SyntaxKind[] modifiers)
+        public static EnumDeclarationSyntax AddModifiers(this EnumDeclarationSyntax cl, params SyntaxKind[]? modifiers)
         {
-            if (modifiers == null)
+            if (modifiers is null)
                 return cl;
             return cl.AddModifiers(modifiers.Select(x => SyntaxFactory.Token(x)).ToArray());
         }
-        
-        
 
         public static string WithLowerFirst(this string s)
         {
@@ -58,7 +56,7 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             return char.ToLowerInvariant(s[0]) + s.Substring(1);
         }
 
-        public static ExpressionSyntax MemberAccess(params string[] identifiers)
+        public static ExpressionSyntax MemberAccess(params string[]? identifiers)
         {
             if (identifiers == null || identifiers.Length == 0)
                 throw new ArgumentException();
@@ -96,4 +94,4 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
                 ? s.Substring(prefix.Length)
                 : s;
     }
-}
\ No newline at end of file
+}
diff --git a/src/tools/DevGenerators/CompositionGenerator/Generator.Utils.cs b/src/tools/DevGenerators/CompositionGenerator/Generator.Utils.cs
index b53c247991..16aa15d95a 100644
--- a/src/tools/DevGenerators/CompositionGenerator/Generator.Utils.cs
+++ b/src/tools/DevGenerators/CompositionGenerator/Generator.Utils.cs
@@ -54,7 +54,7 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
         FieldDeclarationSyntax DeclareField(string type, string name, params SyntaxKind[] modifiers) =>
             DeclareField(type, name, null, modifiers);
 
-        FieldDeclarationSyntax DeclareField(string type, string name, EqualsValueClauseSyntax initializer,
+        FieldDeclarationSyntax DeclareField(string type, string name, EqualsValueClauseSyntax? initializer,
             params SyntaxKind[] modifiers) =>
             FieldDeclaration(
                     VariableDeclaration(ParseTypeName(type),
@@ -63,4 +63,4 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
                 .WithSemicolonToken(Semicolon())
                 .WithModifiers(TokenList(modifiers.Select(x => Token(x))));
     }
-}
\ No newline at end of file
+}
diff --git a/src/tools/DevGenerators/CompositionGenerator/Generator.cs b/src/tools/DevGenerators/CompositionGenerator/Generator.cs
index 18f1d1c1e5..cbcc55ada0 100644
--- a/src/tools/DevGenerators/CompositionGenerator/Generator.cs
+++ b/src/tools/DevGenerators/CompositionGenerator/Generator.cs
@@ -37,8 +37,8 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
 
 
 
-        string ServerName(string c) => c != null ? ("Server" + c) : "ServerObject";
-        string ChangesName(string c) => c != null ? (c + "Changes") : "ChangeSet";
+        string ServerName(string? c) => c != null ? ("Server" + c) : "ServerObject";
+        string ChangesName(string? c) => c != null ? (c + "Changes") : "ChangeSet";
         string ChangedFieldsTypeName(GClass c) => c.Name + "ChangedFields";
         string ChangedFieldsFieldName(GClass c) =>  "_changedFieldsOf" + c.Name;
         string PropertyBackingFieldName(GProperty prop) => "_" + prop.Name.WithLowerFirst();
@@ -298,10 +298,10 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
             if(cl.Implements.Count > 0)
                 foreach (var impl in cl.Implements)
                 {
-                    client = client.WithBaseList(client.BaseList.AddTypes(SimpleBaseType(ParseTypeName(impl.Name))));
+                    client = client.WithBaseList(client.BaseList?.AddTypes(SimpleBaseType(ParseTypeName(impl.Name))));
                     if (impl.ServerName != null)
                         server = server.WithBaseList(
-                            server.BaseList.AddTypes(SimpleBaseType(ParseTypeName(impl.ServerName))));
+                            server.BaseList?.AddTypes(SimpleBaseType(ParseTypeName(impl.ServerName))));
 
                     client = client.AddMembers(
                         ParseMemberDeclaration($"{impl.ServerName} {impl.Name}.Server => Server;"));
@@ -527,7 +527,7 @@ var changed = reader.Read<{ChangedFieldsTypeName(cl)}>();
             body = body.AddStatements(
                 ParseStatement("return base.GetPropertyForAnimation(name);"));
             var method = ((MethodDeclarationSyntax) ParseMemberDeclaration(
-                    $"public override Avalonia.Rendering.Composition.Expressions.ExpressionVariant GetPropertyForAnimation(string name){{}}"))
+                    $"public override Avalonia.Rendering.Composition.Expressions.ExpressionVariant GetPropertyForAnimation(string name){{}}")!)
                 .WithBody(body);
 
             return cl.AddMembers(method);
@@ -540,7 +540,7 @@ var changed = reader.Read<{ChangedFieldsTypeName(cl)}>();
             body = body.AddStatements(
                 ParseStatement("return base.GetCompositionProperty(name);"));
             var method = ((MethodDeclarationSyntax)ParseMemberDeclaration(
-                    $"public override CompositionProperty? GetCompositionProperty(string name){{}}"))
+                    $"public override CompositionProperty? GetCompositionProperty(string name){{}}")!)
                 .WithBody(body);
 
             return cl.AddMembers(method);
@@ -559,11 +559,11 @@ var changed = reader.Read<{ChangedFieldsTypeName(cl)}>();
             );
             return cl.AddMembers(
                 ((MethodDeclarationSyntax) ParseMemberDeclaration(
-                    "internal override void StartAnimation(string propertyName, CompositionAnimation animation, Avalonia.Rendering.Composition.Expressions.ExpressionVariant? finalValue){}"))
+                    "internal override void StartAnimation(string propertyName, CompositionAnimation animation, Avalonia.Rendering.Composition.Expressions.ExpressionVariant? finalValue){}")!)
                 .WithBody(body));
 
 
         }
         
     }
-}
\ No newline at end of file
+}
diff --git a/src/tools/DevGenerators/DevGenerators.csproj b/src/tools/DevGenerators/DevGenerators.csproj
index 30da940514..069ff159fc 100644
--- a/src/tools/DevGenerators/DevGenerators.csproj
+++ b/src/tools/DevGenerators/DevGenerators.csproj
@@ -4,6 +4,7 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>
+    <LangVersion>10</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/tools/DevGenerators/GetProcAddressInitialization.cs b/src/tools/DevGenerators/GetProcAddressInitialization.cs
index c7d03a9b50..aedc13e7f6 100644
--- a/src/tools/DevGenerators/GetProcAddressInitialization.cs
+++ b/src/tools/DevGenerators/GetProcAddressInitialization.cs
@@ -131,10 +131,13 @@ public class GetProcAddressInitializationGenerator : IIncrementalGenerator
                                     .Append(".GetProcAddress(")
                                     .Append("getProcAddress, ")
                                     .Append(contextName);
-                                
-                                var syntaxNode = (AttributeSyntax)attr.ApplicationSyntaxReference.GetSyntax();
-                                foreach (var arg in syntaxNode.ArgumentList.Arguments)
-                                    initializeBody.Append(", ").Append(arg.GetText());
+
+                                if (attr.ApplicationSyntaxReference?.GetSyntax() is AttributeSyntax syntaxNode 
+                                    && syntaxNode.ArgumentList is { })
+                                {
+                                    foreach (var arg in syntaxNode.ArgumentList.Arguments)
+                                        initializeBody.Append(", ").Append(arg.GetText());
+                                }
                                 initializeBody.AppendLine(");");
                             }
                         }
diff --git a/tests/Avalonia.Controls.UnitTests/BorderTests.cs b/tests/Avalonia.Controls.UnitTests/BorderTests.cs
index 7af7d1cee2..e9ddc8e8a3 100644
--- a/tests/Avalonia.Controls.UnitTests/BorderTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/BorderTests.cs
@@ -78,7 +78,7 @@ namespace Avalonia.Controls.UnitTests
                     }
                 };
 
-                var root = CreatedRoot(1.5, target);
+                var root = CreateRoot(1.5, target);
 
                 root.LayoutManager.ExecuteInitialLayoutPass();
 
@@ -101,7 +101,7 @@ namespace Avalonia.Controls.UnitTests
                     }
                 };
 
-                var root = CreatedRoot(1.5, target);
+                var root = CreateRoot(1.5, target);
 
                 root.LayoutManager.ExecuteInitialLayoutPass();
 
@@ -111,7 +111,58 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Equal(new Size(104, 104), target.DesiredSize);
             }
 
-            private static TestRoot CreatedRoot(
+            [Fact]
+            public void Measure_Arranges_Child_To_Rounded_BorderThickness()
+            {
+                Canvas child;
+                var target = new Border
+                {
+                    BorderThickness = new Thickness(1),
+                    Width = 82,
+                    Height = 82,
+                    Child = child = new Canvas(),
+                };
+
+                var root = CreateRoot(1.5, target);
+
+                root.LayoutManager.ExecuteInitialLayoutPass();
+
+                // - 1 pixel border thickness is rounded up to 1.3333; for both sides it is 2.6666
+                // - Size of 82 needs no rounding
+                // - Minus border thickness, space for child is 82 - 2.6666 = 79.3333
+                Assert.Equal(1.3333, child.Bounds.Left, 3);
+                Assert.Equal(1.3333, child.Bounds.Top, 3);
+                Assert.Equal(79.3333, child.Bounds.Width, 3);
+                Assert.Equal(79.3333, child.Bounds.Height, 3);
+            }
+
+            [Fact]
+            public void Measure_Arranges_Child_With_Rounded_Margin()
+            {
+                Border child;
+                var target = new Border
+                {
+                    Width = 220,
+                    Height = 220,
+                    Child = child = new Border
+                    {
+                        Margin = new Thickness(0, 25, 25, 25),
+                    },
+                };
+
+                var root = CreateRoot(1.5, target);
+
+                root.LayoutManager.ExecuteInitialLayoutPass();
+
+                // - 25 margin gets rounded up to 25.3333
+                // - Size of 220 needs no rounding
+                Assert.Equal(0, child.Bounds.Left, 3);
+                Assert.Equal(25.3333, child.Bounds.Top, 3);
+                Assert.Equal(194.6666, child.Bounds.Width, 3);
+                Assert.Equal(169.3333, child.Bounds.Height, 3);
+            }
+
+            private static TestRoot CreateRoot(
                 double scaling,
                 Control child,
                 Size? constraint = null)
diff --git a/tests/Avalonia.Controls.UnitTests/DatePickerTests.cs b/tests/Avalonia.Controls.UnitTests/DatePickerTests.cs
index 3105263290..8271dde3f6 100644
--- a/tests/Avalonia.Controls.UnitTests/DatePickerTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/DatePickerTests.cs
@@ -55,7 +55,7 @@ namespace Avalonia.Controls.UnitTests
 
                 for(int i = 0; i < container.Children.Count; i++)
                 {
-                    if(container.Children[i] is TextBlock tb && tb.Name == "DayText")
+                    if(container.Children[i] is TextBlock tb && tb.Name == "PART_DayTextBlock")
                     {
                         dayText = tb;
                         break;
@@ -93,7 +93,7 @@ namespace Avalonia.Controls.UnitTests
 
                 for (int i = 0; i < container.Children.Count; i++)
                 {
-                    if (container.Children[i] is TextBlock tb && tb.Name == "MonthText")
+                    if (container.Children[i] is TextBlock tb && tb.Name == "PART_MonthTextBlock")
                     {
                         monthText = tb;
                         break;
@@ -131,7 +131,7 @@ namespace Avalonia.Controls.UnitTests
 
                 for (int i = 0; i < container.Children.Count; i++)
                 {
-                    if (container.Children[i] is TextBlock tb && tb.Name == "YearText")
+                    if (container.Children[i] is TextBlock tb && tb.Name == "PART_YearTextBlock")
                     {
                         yearText = tb;
                         break;
@@ -171,15 +171,15 @@ namespace Avalonia.Controls.UnitTests
 
                 for (int i = 0; i < container.Children.Count; i++)
                 {
-                    if (container.Children[i] is TextBlock tb && tb.Name == "YearText")
+                    if (container.Children[i] is TextBlock tb && tb.Name == "PART_YearTextBlock")
                     {
                         yearText = tb;
                     }
-                    else if (container.Children[i] is TextBlock tb1 && tb1.Name == "MonthText")
+                    else if (container.Children[i] is TextBlock tb1 && tb1.Name == "PART_MonthTextBlock")
                     {
                         monthText = tb1;
                     }
-                    else if (container.Children[i] is TextBlock tb2 && tb2.Name == "DayText")
+                    else if (container.Children[i] is TextBlock tb2 && tb2.Name == "PART_DayTextBlock")
                     {
                         dayText = tb2;
                     }
@@ -218,31 +218,31 @@ namespace Avalonia.Controls.UnitTests
                 //Skip contentpresenter
                 var flyoutButton = new Button
                 {
-                    Name = "FlyoutButton"
+                    Name = "PART_FlyoutButton"
                 }.RegisterInNameScope(scope);
                 var contentGrid = new Grid
                 {
-                    Name = "ButtonContentGrid"
+                    Name = "PART_ButtonContentGrid"
                 }.RegisterInNameScope(scope);
                 var dayText = new TextBlock
                 {
-                    Name = "DayText"
+                    Name = "PART_DayTextBlock"
                 }.RegisterInNameScope(scope);
                 var monthText = new TextBlock
                 {
-                    Name = "MonthText"
+                    Name = "PART_MonthTextBlock"
                 }.RegisterInNameScope(scope);
                 var yearText = new TextBlock
                 {
-                    Name = "YearText"
+                    Name = "PART_YearTextBlock"
                 }.RegisterInNameScope(scope);
                 var firstSpacer = new Rectangle
                 {
-                    Name = "FirstSpacer"
+                    Name = "PART_FirstSpacer"
                 }.RegisterInNameScope(scope);
                 var secondSpacer = new Rectangle
                 {
-                    Name = "SecondSpacer"
+                    Name = "PART_SecondSpacer"
                 }.RegisterInNameScope(scope);
                
                 contentGrid.Children.AddRange(new IControl[] { dayText, monthText, yearText, firstSpacer, secondSpacer });
diff --git a/tests/Avalonia.Controls.UnitTests/TimePickerTests.cs b/tests/Avalonia.Controls.UnitTests/TimePickerTests.cs
index c39a963dae..1c2b49dc7d 100644
--- a/tests/Avalonia.Controls.UnitTests/TimePickerTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TimePickerTests.cs
@@ -114,52 +114,52 @@ namespace Avalonia.Controls.UnitTests
                 //Skip contentpresenter
                 var flyoutButton = new Button
                 {
-                    Name = "FlyoutButton"
+                    Name = "PART_FlyoutButton"
                 }.RegisterInNameScope(scope);
                 var contentGrid = new Grid
                 {
-                    Name = "FlyoutButtonContentGrid"
+                    Name = "PART_FlyoutButtonContentGrid"
                 }.RegisterInNameScope(scope);
 
                 var firstPickerHost = new Border
                 {
-                    Name = "FirstPickerHost",
+                    Name = "PART_FirstPickerHost",
                     Child = new TextBlock
                     {
-                        Name = "HourTextBlock"
+                        Name = "PART_HourTextBlock"
                     }.RegisterInNameScope(scope)
                 }.RegisterInNameScope(scope);
                 Grid.SetColumn(firstPickerHost, 0);
 
                 var secondPickerHost = new Border
                 {
-                    Name = "SecondPickerHost",
+                    Name = "PART_SecondPickerHost",
                     Child = new TextBlock
                     {
-                        Name = "MinuteTextBlock"
+                        Name = "PART_MinuteTextBlock"
                     }.RegisterInNameScope(scope)
                 }.RegisterInNameScope(scope);
                 Grid.SetColumn(secondPickerHost, 2);
 
                 var thirdPickerHost = new Border
                 {
-                    Name = "ThirdPickerHost",
+                    Name = "PART_ThirdPickerHost",
                     Child = new TextBlock
                     {
-                        Name = "PeriodTextBlock"
+                        Name = "PART_PeriodTextBlock"
                     }.RegisterInNameScope(scope)
                 }.RegisterInNameScope(scope);
                 Grid.SetColumn(thirdPickerHost, 4);
 
                 var firstSpacer = new Rectangle
                 {
-                    Name = "FirstColumnDivider"
+                    Name = "PART_FirstColumnDivider"
                 }.RegisterInNameScope(scope);
                 Grid.SetColumn(firstSpacer, 1);
 
                 var secondSpacer = new Rectangle
                 {
-                    Name = "SecondColumnDivider"
+                    Name = "PART_SecondColumnDivider"
                 }.RegisterInNameScope(scope);
                 Grid.SetColumn(secondSpacer, 3);