If you start a free zetaboards forum then it uses CSS so you can mess with the forum to learn. Its not that hard if you already are fairly good with HTML and JAVASCRIPT
I learn best by example, like go to csszengarden.com download the css stylesheets and mess around with it to see how it effects the page. But you need to know a bit about css before doing so otherwise it looks like gibberish.
www.web-design-wiki.com its like Wikipedia with lessons in all web site designing tutorial HTML, css, php, java script and much more its in an easy and professional way