CSS, or Cascading Style Sheets, are what make this site look cool, with its drop shadows, and the bar on the right. Javascript is a scripting language that your browser understands, and on this blog is used to make the comment box pop-up.
There are some pretty nifty tricks that can be done when the two are combined (I don’t do any at the moment), and it’s often called DHTML. I read a cool article the other day which showed how to get rounded corners on boxes combining CSS and JS. That may sound simple, but it’s a pretty impressive piece of work.
Here are some examples:
