public static async Task SlideAndFadeDownToBottomAsync(this FrameworkElement element, float duration, bool keepMargin = true, int height = 0)
{
var sb = new Storyboard();
sb.AddSlideBottomDown(duration, height == 0 ? element.ActualHeight : height, .9f, keepMargin);
sb.AddFadeOut(duration);
await DoAnimation(element, duration, sb);
element.Visibility = Visibility.Hidden;
}