Are you being selective enough with your CSS? Maybe too much? CSS Selectors are the basis of good CSS. Inappropriate Selector choice is one of the most common sources of problems I find when troubleshooting CSS. The best strategy I know of is to start simple, and build on it. Don't start with obscure Class names, start with the type selectors. How can you define a Class meant to apply to paragraphs, if you haven't defined paragraphs? Define the basic HTML your site is built from before you add anything else.
For the sake of this discussion, let's define some simple HTML.