Well, a few behind the scenes clutter-removals and broken markup fixes have restored this rails blog to being XHTML valid and CSS valid. If you don't currently have a blog or a website but are looking to build one, I highly recommend checking out this amazing reference for CSS specifications. This will save you worlds of hurt later and can also teach you some pretty amazing styling techniques to make your website really rock the web 2.0 landscape!
Testing your websites CSS Validity
To test the correctness of your css (stylesheets) you can plugin your website in here: http://jigsaw.w3.org/css-validator/validator?uri=http://yourwebsite.com/
Testing your websites XHTML Validity
I also highly recommend checking your websites xhtml validity since it will help you spot errors in your site that you had no idea about! Let a computer do the dirty-work for you rather then straining your eyes over mountains of html. You can check your xhtml validity here: http://validator.w3.org/check?uri=http://yourwebsite.com/ Good luck!