Firebug firebug firebug: http://www.getfirebug.com/

This brilliant Firefox extension is how I learned CSS. Click the "inspect" button, then click any page element, and it'll show you all the CSS rules being applied to that element. It'll also highlight the margin+padding so you can wrap your head around the box model.

Best of all, you can change CSS properties on the fly. Naturally, the best way to learn is to hack up someone else's CSS, so go to a site you like the looks of, and play with the styling.

Soon, you'll be thinking to yourself "man, this isn't complicated at all!"

And then you will open your page in IE 6.

And then you will punch a hole in the wall.