Cascading Style Sheets or (CSS) as they are commonly referred to are a web standard designed to allow the seperation of content and design.

You specify a set of classes which define various attributes of elements. These classes can be defined in an external file which can then be linked in to all of the pages on your site, allowing you to make global changes to the look of your site with one simple edit.

Cascading Style Sheets are currently in their second? or third revision and the amount of stuff that you can do with them is getting cooler all the time.

• http://www.meyerweb.com/eric/css/edge/ - A very cool site showing heaps of things that you can do with CSS. (Also tests your browsers compatability with the standards)
• http://jigsaw.w3.org/css-validator/ - 3wc provides a tool that you can use to validate CSS scripts.
• http://www.w3.org/TR/REC-CSS2/ - Cascading Styel Sheets level 2 specification (I believe this is the current one)
• http://devedge.netscape.com/toolbox/sidebars/ - Devedge has some very good quick references.