It is really complicated, I think, at least for me! I havn't learnt CSS before, therefore, it took me much time to change the default CSS style to the current one.
Here is some useful site that I visit on a regular basis :
456 Berea StreetA personal blog that concerns CSS.
W3Schools
Huge resources including CSS tutorial with examples, quizzes, references in this offical site.HTML dog
HTML and CSS Tutorials, References. This is the first site I refered to when I plan to study HTML and CSS.