So you think you know CSS? Take your CSS skills to the next level and learn to write organized and optimized CSS that will improve the maintainability, performance, and appearance of your work. You'll learn how document flow and CSS positioning schemes will help you make your documents more accessible. You'll discover the great styling possibilities of CSS paired with semantic structures like Microformats and RDFa, while enriching the self-describing semantics of XHTML content. Learn how to group logically related declarations, minify style sheets, and prevent performance bottle necks such as reflows and repaints. With support for CSS enjoying unprecedented ubiquity, you can finally use such features as generated content, complex selector chains, and CSS3's visual properties, like box-shadow, in your projects.
The best CSS book I have come across, so far. It offers an in-depth understanding of how CSS works, starting from the very basics and continuing with more advanced topics, including: optimisations, good coding principles, ways to handle various media types (web,mobile,printing, for people with disabilities) and some historical context in the for of what, when and why . I just loved those "brief histories" included in every section. If you want a basic CSS book with examples, try to find something else. If you want a book that looks into CSS into depth, then this is the book that you are looking for.
May already be obsolete, but goes through a lot of the more esoteric css that is necessary for print, mobile, and written at a time transitioning from CSS2 to CSS3.