Making objects cast shadows with the Shadow inspector
Use the Shadow inspector to drop a shadow behind the selected objects.
The Shadow checkbox determines whether the object should cast a shadow. When it's selected, controls become available for changing the appearance of the shadow. 
Drag the blur slider to make the shadow sharper or fuzzier. 
Click a button to choose whether the shadow appears in front of objects or behind objects on the same layer. If you choose to let shadows appear in front of objects on the same layer, the ordering of objects matters; you can reorder objects with the Bring and Send commands in the Arrange menu. 
Drag the crosshair in the offset control or enter numbers in the offset fields to set how far away from the object the shadow should fall. 
Click the color well in the upper-right to choose a color for the shadow; partially transparent black tends to work best.