CSS stands for Cascading Style Sheets, and determines how websites look. It's different to HTML, which controls what a website contains, allowing for a separation of content and presentation.

You can see how the site looks without any CSS at all by going to (in Firefo View > Page Style, and selecting "No Style".

A really good example of the power of CSS is CSS Zen Garden. Select some of the designs from the menu on the left. The HTML in every case is exactly the same, the only thing which changes is the CSS which determines how that HTML is presented.

The custom CSS functionality I've added will allow you to customise almost any aspect of how RAFO looks, from colours and fonts through to where things are positioned.

Hope that helps!