There's a few Mac tools that I've played around with.
However, like DW's good WYSIWYG editor, I've drifted back towards hand-coding.
I suspect it will be a few years before CSS is ready for true "point and click" editing. The browser incompatibilities are just WAY too nasty. I spend twice as much time debugging CSS as I spend writing it.
For that, I need a text editor and some test browsers. Presentation simulations (like DreamWeaver's) are completely worthless, if not downright dangerous. You need to actually test the CSS in your target browsers.
The WebDeveloper Toolbar [chrispederick.com] for Firefox is amazing. It allows you to edit the CSS for ANY site, in-place. Great learning tool.
I would suggest starting with DW's stylemaker, and then tweaking by hand; either with DW's text editor, or an external one. I actually prefer using DW's editor over BBEdit (my usual editor), because it has better support for hinting.
However, you have GOT to test with multiple browsers. There's absolutely no substitute for that.
A basic rule of thumb for me is the same as I use for graphic layout: Put it all in, then keep removing things until you are at the bare minimum you need to support. This tends to deliver very good, simple, robust, compatible code.
That W3School link is great. They let you try out the CSS in place.