If you want to apply the drop shadow effect to your UI Element:

Create a System.Windows.Media.Effects.DropShadowBitmapEffect element, and assign it to the BitmapEffect property of the element you want to have a shadow. Use the Color property of the DropShadowBitmapEffect element to define the color of the shadow and the ShadowDepth property to define the size of the shadow on the target element.