Also referred to simply as CSS, Cascading Style Sheets are used to define the look and feel of a web site outside of the actual HTML file(s) of the site. In recent years, CSS has replaced tables and other HTML-based methods for formatting and laying out websites. The benefits to using CSS are many, but some of the most important are the simplification of a site’s HTML files (which can actually increase search engine rankings) and the ability to completely change the style of a site by changing just one file, without having to make changes to content.