DropShadow is an extender which applies a "Drop Shadow" to a Panel.  It allows you to specify how wide the shadow is as well as how opaque it is, or if you would like rounded corners.  For pages that allow the user to move or resize the panel, the DropShadow has a mode that will resize/reposition it to match that of the target panel at run time.

The control above is initialized with this code:

 <ajaxToolkit:DropShadowExtender ID="dse" runat="server"
        TargetControlID="Panel1" 
        Opacity=".8" 
        Rounded="true"
        TrackPosition="true" />

• TargetControlID - The ID of the button or link for this extender to operate on
• Width - The width, in pixels of the drop shadow. Default value is 5.
• Opacity - The opacity of the drop shadow, from 0 (fully transparent) to 1.0 (fully opaque). The default value is .5.
• TrackPosition - Whether the drop shadow should track the position of the panel it is attached to. Use this if the panel is absolutely positioned or will otherwise move.
• Rounded - Set to true to set rounded corners on the target and the shadow. Default is false.