Stunning CSS3: Project-based Guide to the Latest in CSS by Zoe Mickley Gillenwater
Chapter one is a great introduction to the state of the world, clearly describing vendor prefixes, progressive enhancement and the state of browser support for CSS 3, with additional discussion of how to structure your CSS file to avoid slowing the browser down.
Chapter 6 discusses different screen size, illustrating the use of media queries to target CSS at particular types of device, and the final chapter discusses the new layouts of CSS 3 including the flexible box model.
I thought that reading this book was a really good way to catch up with the new features of CSS 3, and get a clear idea of how these features could be used for real. The examples are good and thorough (even though I didn’t download them and actually do the exercises) and the book is really well written. Brilliant!