Good article. I've had that one bookmarked for a while, and it has saved me more than one headache. If you don't understand stacking context and z-index is not working as you expect, you need to go read this.
This saved my ass, and my head from exploding. I found it while dealing with an obnoxious situation where a sibling element's background was causing background-color to not work at all when positioned behind said background-color having element. And it was fascinating to read about how z-index works. One of those little-known quirks to CSS that everybody really should know.
