Handy CSS Cheat Sheet to keep your practice true
 

CSS has transformed the web. Long gone are the days of putting everything in table cells and trying to tweek layout using   characters. CSS is not always easy to keep straight. To help you keep key CSS concepts in mind, we've prepared a handy QuickSheet covering key CSS concepts on one page for quick reference. Feel free to download this QuickSheet and use it in your practice.

The QuickSheet is provided in three formats. A PDF and a PNG image format (make it a wallpaper image for your laptop!).
 

The PDF references some useful sites. W3C Schools and Sitepoint are good CSS reference sites. Firebug is a browser add on that facilitates the debugging and editing of a site's CSS, HTML, and JavaScript. And if you're not developing on a Mac, you should get Safari for PC and test your sites with Safari.