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 Web 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, <font> tags, tables, and spacer GIFs - allows for
faster downloads, streamlined site maintenance, and instantaneous global
control of design attributes across multiple pages.