Hi Edwin.
Firebug is a very useful tool to play around with everything about CSS.
You can look and tweak any element in Your page and find what You need to accomplish what You want.
Use Your own CSS-file, don't mess with th existing ones - mmm like I did at first
And after years of windows-programming: Do not put too much energy on (pixel-level) layout. It us not worth the effort because You just can not control all the browsers in the world. Well, that's my conclusion anyway.
:: rainer