XHTML

If your looking for a more advanced CSS book, this one is definitely worth looking into.

As I have mentioned before in other reviews, I always like it when the author tells me up front who the target audience is. In this case, the first sentence in "What this book is not" states "This book is not an introduction to CSS." I like this type of straightforward notice. It definitely helps keep a novice from getting in over their head or a guru from getting bored.