UI adjustment

Pixiview.iOS/Renderers/AppShellRenderer.cs

@@ -51,6 +51,11 @@ namespace Pixiview.iOS.Renderers
         {
             return new AppShellTabBarAppearanceTracker();
         }
+
+        protected override void UpdateBackgroundColor()
+        {
+            NativeView.BackgroundColor = Color.Transparent.ToUIColor();
+        }
     }
 
     public class AppShellItemTransition : IShellItemTransition