A skin is a definition of styles applied to the server controls in your ASP.NET page.
Skins can work in conjunction with CSS files or images.
The skin file can have any name, but it must have a .skin file extension.
The Summer.skin file.
Control definitions must contain the Runat="server" attribute.
No ID attribute is specified in the skinned version of the control.
Using the Summer theme in an ASP.NET page.
<%@ Page Language="VB" Theme="Summer" %>