CSS stands for Cascading Style Sheets. CSS allows a web designer to separate content of a page from visual display of a page. Instead of using font and center tags and align attribute, stylesheets allows a designer to specify alignment and font attributes away from the content.
All the URI camp websites use CSS for their layout, they have an external stylesheet that applies to all pages to keep the content on the page organized into sections. These sections can be moved or have their color changed by simply changing the stylesheet element that applies to their position or display.