CSS: The Definitive Guide. 4-ed. E. Meyer, E. Weyl

 If you are a web designer or document author interested in sophisticated page styling, improved accessibility, and saving time and effort, this book is for you. All you really need to know before starting the book is HTML 4.0. The better you know HTML, the better prepared you’ll be, but it is not a requirement. You will need to know very little else to follow this book.
 This fourth edition of the book was finished in mid-2017 and does its best to reflect the state of CSS at that time. The assumption is that anything covered in detail either had wide browser support at the time of writing or was known to be coming soon after publication. CSS features which were still being developed, or were known to have support dropping soon, are not covered here.