Working with new standards on the web sometimes requires some tools to make transition easier. The web started off on the Mac with early HTML editors like Claris HomePage and Adobe PageMill and later Adobe GoLive and Macromedia Dreamweaver. Increasingly, these tools are adopting CSS support but they are not made for primarily focussing on CSS.
An exception is CSSEdit. It can load CSS directly from the web and of course you can use it to directly edit CSS files on your local disk as well. While I still prefer to hand-code my CSS and use BBEdit for it, it might be a helper for those who are still fighting with the basic rules of CSS. With $14.99, it is pretty cheap and is good add-on for your personal web toolbox.
By the way, the CSSEdit Home Page shows some pretty nifty use of CSS to learn from. Look at the page with a modern web browser like Mozilla or Safari to get the scoop.