CSS is an extremely useful form of web page formatting.
It is basically a way of telling a large amount of web pages how to look, so that when you enter information for a new page on your extensive website, you don't have to re-code the whole thing over again to make it look the same, you merely have to "call" back to your CSS sheet.
This has great advantage over the normal HTML formatting, as you can see.
For instance, this site, blogger, uses CSS so that when you make several blog posts, all their pages look the same, and when you want to edit what they look like, you only have to edit one pice of code to effect the whole lot. you can change fonts, colours and set up to suit your needs.
The short comings of this system is that you cant have one blog post looking different to another, for visual reasons or otherwise.
Accessibility is very important, as it allows the blind or sight impaired to have words read to them, or have fonts larger so that they may read them with greater ease.
Things i have done to my blog with CSS editing:
changed colours and font, also editing margins and the like, giving my page greater (though minimal) space.
Todays picture is what Encyclopedia Dramatica has to say about CSS
"Never compromise, even in the face of armageddon."