protected override void OnRender(DrawingContext drawingContext)
 {
     base.OnRender(drawingContext);
     if (Stack == null) Stack = DemoStack;
     var y = 0;
     if (Stack.Any())
     {
         foreach (var card in Stack)
         {
             var cardRect = new Rect(0, y, Width, Width * 1.5);
             drawingContext.DrawCard(card, cardRect);
             y += card.Visible ? 20 : 10;
         }
     }
     else
     {
         DrawEmptyStack(drawingContext);
     }
 }