A global theme is a theme that you can apply to all the Web sites on a server. Global themes allow you to define an overall look for your domain when you maintain multiple Web sites on the same server. Global themes are like page themes in that they include property settings, style sheet settings, and graphics. However, global themes are stored in a folder named \Themes that is global to the Web server. Any Web site on the server, and any page in any Web site, can reference a global theme
To create a global theme:
2. Create a theme folder as a subfolder of the Themes folder. The name of the subfolder is the name of the theme. For example, to create a global theme named BlueTheme, create a folder named ...\Themes\BlueTheme.
3.Add files to your new folder for skins, style sheets, and images that make up the theme.
For more information about creating a global theme folder, see How to: Define ASP.NET Themes.