i'm going to beat a dead horse here, but as always i think the best way to learn (esp. html and css) is to hack through someone else's code. i'm completely self-taught - not that i have much to show for it - through precious few books but a lot of "view source".
so just try wading through some else's stylesheet. and if they don't have the code right there in the course, but rather have a link to a .css file, just copy and paste the file name (mycss.css) and add it to the end of the address in your browser.
have fun!