What do I need to read to be great at CSS?

A rule of thumb is that the importance of a blog in your feed reader is inversely proportional to their posting cadence. Prioritise the blogs that post only once a month or every couple of weeks over those that post every day or multiple times a day...Building up a large library of sporadically updated blogs is much more useful and much easier to keep up with than trying to keep up with a handful of aggregation sites every day.