pagetta,
CSS can't really "directly" help your on page SEO, per-se.
CSS can help with clean code that loads fast and you have the ability to 'sneak' in key kw elements into your page.
For starters not many people know, or buy into for that matter, that crappy code can really screw up a spider when he goes to read your page. Plus a spider doesn't
always spider a whole page. A spider will read a page just like a browser. If a browser gets hung up on your page(s) chances are that a spider will too. So if you have a ton of wysiwyg crap along with a miles worth of crap in the head of your document chances are that a spider won't read all the way through the "meat" of your content rich page.
Next you have the ability to format heading tags to match your site. We all know that your kws should be in heading tags. But sometimes sticking in heading tags throws off our pages. With css we can format these to match.
Same thing with bolding but without the bolding effect.
Now if you were a hacker "SEOist" you could make font color and background color the same.
However I do NOT recommend this! I've just seen it done.
There are a few other things but it all basically boils down to formatting and creating clean coded pages. Atleast that I know of. <smile>
So what you said about basic formatting for text is a great practice and keep with it. I use a lot of CSS for my pages but have reverted back to, for the time being, using tables for positioning. I did a few sites in all CSS but checking backwards browser compatibility made me go back to tables. Old netscape browsers did not respond in kind. Yeah I could have made "backup css" and stuff but that's too much for me.
Any clearer?
Chris
Oh. . .this is all mho!