I'm not sure what you mean by a CSS template. I assume that you are referring to a WB template. If so, a good place to start is with the documentation. The Advanced Documentation will specifically discuss modifying templates:
http://help.websitebaker.org/pages/en/advanced-docu.phpOnce you understand the basics, you can modify the generic template or any other template.
If you are referring to CSS and not WB then please do a CSS search on Google.