feat: clean up warnings.

src/Ursa/Controls/ThemeSelector/ThemeSelectorBase.cs

@@ -3,8 +3,6 @@ using Avalonia.Controls;
 using Avalonia.Controls.Primitives;
 using Avalonia.LogicalTree;
 using Avalonia.Styling;
-using Ursa.Common;
-using System;
 
 namespace Ursa.Controls;
 
@@ -61,7 +59,7 @@ public abstract class ThemeSelectorBase: TemplatedControl
         }
     }
 
-    private void OnScopeThemeChanged(object sender, System.EventArgs e)
+    private void OnScopeThemeChanged(object? sender, System.EventArgs e)
     {
         _syncFromScope = true;
         if (this.TargetScope is { } target)
@@ -149,7 +147,6 @@ public abstract class ThemeSelectorBase: TemplatedControl
         if (_application is not null)
         {
             _application.RequestedThemeVariant = newTheme;
-            return;
         }
     }
 }