Here is a link to a thread that explains the most common things that can go wrong with that exercise: http://discuss.codecademy.com/t/exercises-6-and-8-common-problems/9999
If you can't get unstuck using that, then post your code here and I'll help you spot the problem.
Here is what I need to troubleshoot this exercise:
<head> ... </head> element from your index.html file.
- All of your main.css file.
If you need it: How to post code in this forum.