I was at a web conference the last few days where mention was made of Dave Shea's CSS Zen Garden, now 12 years old and still shining. The idea is for anyone to apply their own styles to a page of identical content. Not only is it a great way to explore just what YOU can do with CSS, it's also a great display of what others can do. To me, it bridges that gap between book learning and gettin'g out and DOing.

Using both works best in my opinion :) Sure, lots of sites with tutorials etc. But for deep knowledge, a book can be mighty handy I think.

Books of CSS? Actually, I've seen some titles from "famous" designers, but what I've learned is that you simply learn more with CSS oriented sites than any book. Learn how to use the browser's console to mess with any page, (Even this one). Learn the meaning of ID's, classes, conditional CSS, children, parent. and later transitions and animation. Start with the basis and as you get better, search for tutorials to learn more.