// Get a reference to the Button.
Button myButton = new Button();

// Initialize a new DropShadowBitmapEffect that will be applied
// to the Button.
DropShadowBitmapEffect myDropShadowEffect  = new DropShadowBitmapEffect();
// Set the color of the shadow to Black.
Color myShadowColor = new Color();
myShadowColor.ScA = 1;
myShadowColor.ScB  = 0;
myShadowColor.ScG  = 0;
myShadowColor.ScR  = 0;
myDropShadowEffect.Color = myShadowColor;

// Set the direction of where the shadow is cast to 320 degrees.
myDropShadowEffect.Direction = 320; 

// Set the depth of the shadow being cast.
myDropShadowEffect.ShadowDepth = 25; 

// Set the shadow softness to the maximum (range of 0-1).
myDropShadowEffect.Softness = 1;
// Set the shadow opacity to half opaque or in other words - half transparent.
// The range is 0-1.
myDropShadowEffect.Opacity = 0.5; 

// Apply the bitmap effect to the Button.
myButton.BitmapEffect = myDropShadowEffect;