Overview

Cascading Style Sheets (CSS) is a simple mechanism used to style web pages (e.g. fonts, colors, spacing). 

With CSS, style sheets can be created that will define how different elements will appear and can be applied to any web page. This has become the preferred method for controlling the physical presentation of web pages because it is easy to manage with large web sites. Instead of having to update the font on each individual web page, you can just change the style sheet, and all the pages on the site just automatically start using it.

Multiple style sheets can be applied to the same web page. CSS specifies a priority scheme to determine which style rules apply if more than one rule matches against a particular element to provide predictable results.

On your site, there will usually be two style sheets being used: the software's internal style sheet which sets all the defaults by which the interfaces are displayed, and your layout's style sheet which adjusts these defaults to your site's desired settings.