Cascading Style Sheets or CSS as they are more commonly known have been around for many years now and can be used to format your page any way imaginable. CSS is a very easy way to keep you web page consistant with your fonts, colors, and many other aspects. CSS also allows you to get this information in a single file instead across all of your web pages. If you have a 200 + page website and a decision has been made to change the font on the pages from arial to verdana then you would have to manually edit 200+ pages to make tha change. But with CSS all you have to do is change the CSS files, which for a large webpage maybe two or three files, a lot better than 200+ files.