The problem with most such web-based quizzes is that they usually are multiple choice, and tend to focus on syntax rather than application of that syntax in a useful way. While it's good to know that the CSS property used to align text within a block element is "text-align", that's just simple memorization of information that is easily available to you if you happen to forget it.
I'd recommend doing something like:
Go to www.csszengarden.com. Download a copy of the HTML source code they use on all the pages there. Select one of the layouts you like there. Do your best to emulate that layout with your own stylesheet. When done, take a look at the stylesheet that the page's author used and compare his result with yours (and maybe find out how he did that tricky bit you couldn't figure out).