I started learning CSS a couple of years ago from a book which was appropriate to my needs as a beginner at the time. It taught me some very helpful stuff which I have used on web sites. Here is an example:-
Given my current level/lack of ability in CSS, can anyone recommend a book that will take me further?
My two recommendations:
1) The Zen of CSS Design; a fantastic demonstration of what's possible.
2) Pro CSS and HTML Design Patterns; a book that shows you what works reliably in most browsers, rather than everything defined in the various CSS standards.
I would recommend
CSS: The Missing Manual, D S McFarland (2009, but still very relevant)
HTML & CSS: Design and Build Web Sites, Jon Duckett (2011) - a very nice book to own, but not quite as detailed as The Missing Manual.
CSS Mastery: Advanced Web Standards Solutions, Second Edition