Window css class

[Alex]

Is there any way I can set a custom css class through the window manager or on a window itself.

[Obi-Wan Kenobi]

To use a custom CSS skin file you need to disable the built-in skin CSS files by setting EnableEmbeddedSkins property to false. . Also you should manually register the CSS file for your custom skin in the page's HEAD tag.

You can find more in online help.
Hope this helps!