Cascading Style Sheets (CSS) are use to create a set of styles that can be applied to your HTML attributes (fonts, boxes, tables, etc.). It allows you to create clean and fast loading pages that search engines love. It also makes life easier on designers, allowing for a single point of control for all attributes in your pages. Some of the effects that were once done with Javascript can now be done much more effectively with CSS (menu rollovers, for instance)
The following are some layouts that use CSS. Notice that no Javascript is used in any of them.