Recently I came across this very useful site (Web Design in 4 minutes) via a friend of mine (@thedevgirl).

Basically think of this as a game, you keep clicking as it would be an adventure game and you keep going to explore and more details about the beauty of web design. It helped me greatly to put my CSS knowledge into place and revise what is what.

Also the site shares very important details and principles how to build a project or portfolio, so keep on reading and have fun clicking!