I don't see why using CSS Frameworks.
I always do my CSS from scratch, sometimes to remember sometimes i go back to my older CSS styles and look around. And sometimes i just do some testing until I've obtained what i wanted.
EDIT: Just read some of the web standards guidelines and do some experiment and you will get the hand of it..
I did the same and at my first times.. I had some cross-browser issues and other small stuff.
now i'm pretty happy to say that i do cross-browser css, with no big problem.
But if you just need CSS for a project, and you wont be needing CSS again, using a Framework might not be a bad idea.