The book was a bit dated (it only went up to XHTML 1.0 and adamantly stated numerous times there will never be an HTML5) but nonetheless I feel as if I learned a good deal about HTML and CSS.<p>Tips on where to go to learn more? Or how to get better from here? Important things the book might have missed?
Start building stuff. I never learn tools for the sake of the tool; I learn them for the sake of the project I want to use them on. (I exaggerate slightly. Fun is also a big motivator, and some tools are inherently fun. But my main point stands.)
Build something!!! Maybe just a static site or a make your own Posterous or Tumblr theme. This will be a helpful way to apply what you have read. Reading is fine but the best way to learn is to start coding.