There is a lot to learn about Cascading Style Sheets, and sometimes the best way to learn it is with a book. These are some of my favorite CSS books for learning CSS. They work well for beginners, and several of them also provide a lot of information for more advanced CSS designers.
I really enjoy the Missing Manual series. These books make whatever topic they are about much more accessible to the average customer. The CSS Missing Manual covers the basics of Cascading Style Sheets through complex things like CSS layouts. The examples and easy-to-understand explanations make this book a must for CSS beginners.
Some might not agree that this is a great book for learning CSS, but if you learn better by doing then this book is great. Instead of focusing on style properties and syntax, this book dives right into making changes to your Web pages with CSS.
Sometimes you just want to learn something quickly. The Sams Teach Yourself CSS in 24 hours book has all you need to get the basics of CSS down as quickly as possible.
This is the book that I've always recommended to people about CSS. If you can't buy more than one book, then you should buy this one. It's the first and best book on CSS on the market. It's not as well tailored to beginners as some of the others listed, but if you're willing to work a little, it is an unflagging resource. You'll have it on your desk long after the other books are recycled.
Core CSS provides a great reference manual on CSS levels 1 through 3. It includes browser support as well as the basic tag references. This is the perfect book for someone who wants to learn CSS from a very technical standpoint.
I love that this book is in full color. CSS is a designer's language, and color is important to design. If you are a designer who wants to learn CSS, then this book is a great resource. It's not a great book for people who have never done any Web programming or HTML, but if you're slightly more advanced it's a great tool to learn lots of CSS.
People who learn by seeing will love this book. The full color examples make the CSS come alive in the book, and it focuses a lot more on how the pages will look than on the code to create them.