Flex 4: How to apply RectangularDropShadow?

Flex 4: How to apply RectangularDropShadow?

I am new to Flex so there are things that I am not used to. I have added
the RectangularDropShadow in the Declarations tag of a Rect MXML
component. It does not show anything, I am sure there is something more I
should do to apply it to the Rect.
<?xml version="1.0" encoding="utf-8"?>
<s:Rect xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
height="314" width="478">
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects)
here -->
<s:RectangularDropShadow id="cardAreaShadow"
alpha="0.4"
distance="10"
angle="45"
color="#000000" />
</fx:Declarations>
<s:fill>
<s:SolidColor color="#FFFFFF" />
</s:fill>
</s:Rect>