Workaround for the inherited default value bug

src/Avalonia.Controls/ThemeVariantScope.cs

@@ -13,8 +13,7 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<ThemeVariant> ActualThemeVariantProperty =
             AvaloniaProperty.Register<ThemeVariantScope, ThemeVariant>(
                 nameof(ActualThemeVariant),
-                inherits: true,
-                defaultValue: ThemeVariant.Light);
+                inherits: true);
 
         /// <summary>
         /// Defines the <see cref="RequestedThemeVariant"/> property.

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ThemeDictionariesTests.cs

@@ -1,8 +1,12 @@
-using Avalonia.Controls;
+using System.Linq;
+using Avalonia.Controls;
+using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Primitives;
 using Avalonia.Markup.Data;
 using Avalonia.Markup.Xaml.MarkupExtensions;
 using Avalonia.Media;
 using Avalonia.Styling;
+using Avalonia.UnitTests;
 using Moq;
 using Xunit;
 
@@ -444,4 +448,71 @@ public class ThemeDictionariesTests : XamlTestBase
 
         Assert.Equal(Colors.Black, ((ISolidColorBrush)border.Background)!.Color);
     }
+    
+    [Fact]
+    public void Theme_Switch_Works_In_Nested_Scope()
+    {
+        using (UnitTestApplication.Start(TestServices.StyledWindow))
+        {
+            var window = (Window)AvaloniaRuntimeXamlLoader.Load(@"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        RequestedThemeVariant='Dark'>
+    <ThemeVariantScope Name='Scope'>
+        <TextBlock Name='Text' />
+    </ThemeVariantScope>
+</Window>");
+            window.ApplyTemplate();
+
+            var scope = window.FindControl<ThemeVariantScope>("Scope")!;
+            var text = window.FindControl<TextBlock>("Text")!;
+
+            Assert.Equal(ThemeVariant.Dark, text.ActualThemeVariant);
+            Assert.Equal(Color.Parse("#dedede"), ((ISolidColorBrush)text.Foreground!).Color);
+            
+            scope.RequestedThemeVariant = ThemeVariant.Light;
+            Assert.Equal(ThemeVariant.Light, text.ActualThemeVariant);
+            Assert.Equal(Colors.Black, ((ISolidColorBrush)text.Foreground!).Color);
+        }
+    }
+    
+    [Fact]
+    public void Theme_Switch_Works_In_With_Popup()
+    {
+        using (UnitTestApplication.Start(TestServices.StyledWindow))
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(@"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <ThemeVariantScope Name='Scope' RequestedThemeVariant='Dark'>
+        <Popup Name='Popup'>
+            <Border Width='100' Height='100'
+                    Background='{DynamicResource ThemeBackgroundBrush}'>
+            </Border>
+        </Popup>
+    </ThemeVariantScope>
+</Window>");
+                window.Show();
+
+                var scope = window.FindControl<ThemeVariantScope>("Scope")!;
+                var popup = window.FindControl<Popup>("Popup")!;
+                
+                popup.IsOpen = true;
+
+                var border = (Border)popup.Child!;
+
+                Assert.Equal(ThemeVariant.Dark, popup.ActualThemeVariant);
+                Assert.Equal(ThemeVariant.Dark, border.ActualThemeVariant);
+                Assert.Equal(Color.Parse("#282828"), ((ISolidColorBrush)border.Background!).Color);
+                
+                scope.RequestedThemeVariant = ThemeVariant.Light;
+
+                Assert.Equal(ThemeVariant.Light, popup.ActualThemeVariant);
+                Assert.Equal(ThemeVariant.Light, border.ActualThemeVariant);
+                Assert.Equal(Colors.White, ((ISolidColorBrush)border.Background!).Color);
+            }
+        }
+    }
 }