Again, it is important for any web designer to understand who and what w3 is. Well it should be the standard to which you make your webpages. Especially with the launch of I.E. 8 and its amazing similarity to other browsers now that web designers will soon have an easier time and not create I.E. hacks or work arounds.

Well to start here is the CSS validator.

Now there are a few options and you can choose. No one is better than another.

Now there might be a ton of questions about this, but it is most likely better left to the experts, the creators, w3 FAQ.

So you could have googled and received all of the info above, but could you get this!

...

Well I can not really think of a tool for CSS like there is for HTML, but I would recommend getting a program like Microsoft Expressions or the free version - Web Development.