Anyway, as far as styling is concerned, there are two alternate approaches that you can take. Both will work fine:
1) Study CSS carefully and then design you XHTML specifications so that they let you use the styling you like.
2) Make sure your XHTML uses plenty of structural information (a consistent set of classes used frequently) and just assume that when you are done with your XHTML, someone will be able to style it according to your needs.
Even #2 will work fine - CSS is a very powerful tool. It is not all-powerful, there are things that it can't do, and things it can't do without help in the XHTML, but overall, it can do a whole lot. Check the classical site of
CSS Zen Garden to see what I mean - all those different pages actually use the same XHTML markup, only the CSS sheet is different in each of them.