Update tests and designer

src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevelImpl.cs

@@ -58,6 +58,8 @@ namespace Avalonia.Controls.Embedding.Offscreen
 
         public Action<WindowTransparencyLevel>? TransparencyLevelChanged { get; set; }
 
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
         /// <inheritdoc/>
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
 

src/Avalonia.Controls/Platform/ITopLevelImpl.cs

@@ -163,6 +163,12 @@ namespace Avalonia.Platform
         /// </summary>
         WindowTransparencyLevel TransparencyLevel { get; }
 
+        /// <summary>
+        /// Sets the <see cref="PlatformThemeVariant"/> on the frame if it should be dark or light.
+        /// Also applies for the mobile status bar.
+        /// </summary>
+        void SetFrameThemeVariant(PlatformThemeVariant themeVariant);
+        
         /// <summary>
         /// Gets the <see cref="AcrylicPlatformCompensationLevels"/> for the platform.        
         /// </summary>

src/Avalonia.DesignerSupport/Remote/Stubs.cs

@@ -182,7 +182,9 @@ namespace Avalonia.DesignerSupport.Remote
         public bool IsClientAreaExtendedToDecorations { get; }
 
         public bool NeedsManagedDecorations => false;
-        
+
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 1, 1);
     }
 

src/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -345,5 +345,10 @@ namespace Avalonia.Headless
         {
             
         }
+        
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
+        {
+            
+        }
     }
 }

tests/Avalonia.Base.UnitTests/Rendering/CompositorTestsBase.cs

@@ -104,6 +104,8 @@ public class CompositorTestsBase
         }
 
         public WindowTransparencyLevel TransparencyLevel { get; }
+        public void SetFrameThemeVariant(PlatformThemeVariant themeVariant) { }
+
         public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; }
     }