I would say that 75% of the time I have bought a technical book it has turned out to be a disappointment. They are either to basic or way to advanced. So I was really dreading spending money on a CSS book.
I knew the basics of CSS but needed to learn the next step of what to do with it, and personally I hate reading digitized text. I prefer to have physical media in hand. After taking a look at what Amazon had to offer I bought CSS: The Missing Manual by David Sawyer. It had a 4.5 star rating so I took a chance.
What a pleasant surprise this book turned out to be. It had the basics, but the book did an excellent job of teaching what you can do with CSS. There were a lot of exercises that you can see on the fly how your CSS code affected the page.
If I had a complaint, it would be the lack of a complete CSS command reference with a brief explanation of what they do. Still have to rely on The Ultimate CSS Reference for that one.
If you are learning CSS I would suggest taking a look.