CSS WorK
I took a couple of cascading style sheets classes in 2002. The last one, an advanced course taught by Eric A. Meyer, author of "Cascading Syle Sheets: The Definitive Guide", was very challenging and demanding. The course had quite a bit of CSS theory as well as practice that helped me to understand why browsers behave as they do, what should be happening, and how to try to turn things to an advantage.
Topics explored included: how selectors really work, why the cascade and specificity can turn your hair gray, techniques to overcome strangeness in line layout, media-specific and alternate styles, how DOCTYPE switching can make styling easier or harder, and a few ways to sneak past browser bugs without upsetting others.