Panel, Rounded corners Extender and Drop shadow Extender in Microsoft Visual Studio AJAX. Drop Shadow is an extender which applies a Drop Shadow to a Panel. The RoundedCorners extender applies rounded corners to existing elements. You can choose the corners of the target panel that should be rounded by setting the Corners property on the extender to None, TopLeft, TopRight, BottomRight, BottomLeft, Top, Right, Bottom, Left, or All.