What is CSS?

Cascading Style Sheets

A collection of formatting rules that control the appearance of content in a web page.

When you use CSS to format a page, you separate content from presentation. The content of your page--the HTML code--resides in the HTML file itself, while the CSS rules defining the presentation of the code reside in another file (an external style sheet) or in another part of the HTML document (usually the head section). With CSS you have great flexibility and control over the exact appearance of your page, from precise positioning of layout to specific fonts and styles.

A major advantage of CSS is that it provides easy update capability; when you update a CSS rule in one place, the formatting of all the documents that use the defined style are automatically updated to the new style.

The term cascading refers to your ability to apply multiple styles to the same element. For example, you can create one CSS rule to apply color and another to apply margins, and apply them both to the same text on a page. The defined styles "cascade" down to the elements on your web page, ultimately creating the design you want.