In 1996 the W3C introduced Cascading Style Sheets level 1 to help separate Content from Presentation.
xhtml can be used to markup content, CSS used to present that information.
Separating content from layout facilitates the maintenance of web pages.
Now the design of entire web sites can be changed by just a few keystrokes in a single file.
Delivering web pages to other platforms such as PDA's or in other formats, such as print, simply requires a different CSS.
CSS are relatively browser neutral, that is they work pretty much the same way in the major browsers.
Unfortunately no browser is completely compliant with the W3C Standards though most are fairly close.
Users with version 4 browsers and above can take advantage of Cascading Style Sheets
Reference Guides and Resources for CSS
Css Reference - an excellent guide to level 1 CSS
Colours -a list of stylesheet colours, their names and hex values
CSS Example 1 Here is an example of using CSS on plain text.
CSS Example 2 Here is an example of using different CSS on the same content.
Restyling Scrollbars In IE only, you can restyle the Scrollbars and Cursors.
Css Popups Most popups use javascript, these are done with pure css .
CSS Homer Homer drawn with just text and CSS.
CSS House A House drawn with just text and CSS.
Other good resources
Here are some really nice (professionally designed) examples of using different CSS on the same content. http://www.csszengarden.com
www.brainjar.com is a good example of a standards compatible, well designed CSS Web site.
Mastergrid.html Crossbrowser CSS Compatibility Chart - Each Browsers support for CSS
http://www.webreview.com/style/css1/charts/mastergrid.shtml