What Is CSS?
CSS (cascading stylesheets) is a simple mechanism for controlling the style of a web document without compromising its structure. By separating visual design elements (fonts, colors, margins, and so on) from the structural logic of a web page, CSS gives designers the control they crave without sacrificing the integrity of the data, thus maintaining its usability in multiple environments.
In addition, defining typographic design and page layout from within a single, distinct block of code — without having to resort to image maps, tags, tables, and spacer GIFs — allows for faster downloads, streamlined site maintenance, and instantaneous global control of design attributes across multiple pages.
Client-side support for the various CSS properties is uneven, even among browsers that support stylesheets.