I assume you mean you added the selectors to the css, and now you want the portal to render markup that contains the classes/ids to activate the selectors, right?
If that's the case. look at the layout's jsp(s) (depending on what layout you are using), and the renderSet classes (most likely you are using the divRenderer). You can modify the originals, or create your own, and point the portal to use them instead. Check the Theme documentation for many details on how to do all of this....
I'll check it out ;)