It's always a thing I've been fairly weak at - partly because in the past it was of limited use due to stupid browser incompatabilities - but now there's really no excuse for not being a CSS devotee, particularly when trying to design lightweight yet accessible sites. The best turorial I've ever found is at
this site - they have 5 main tutorials which go through many steps and impart knowledge with an almost scary subtelty. Anways,
go there, learn!