CSS

Cascading Style Sheets (CSS) is used by both the authors and readers of web pages to describe colors, layout, fonts, and other aspects of document presentation. It is intended mainly to separate the structure of a web page (written in HTML, XHTML or a related markup language) from its style or the means it looks (written in CSS). This separation can get better accessibility, give more flexibility and control in the requirement of presentational characteristics, and lessen complexity and repetition in the structural content. CSS can as well allow the same web page to be presented in different styles for different applications, like on-screen, in print, by voice (when read out by a speech-based browser or screen reader) and on braille-based devices. Likewise, similiar HTML or XML code can be displayed in different 'skins', color schemes by accessing various CSS files. You may have seen this on sites that let you to customize its colors and look.

CSS can as well be used and interpreted by few browsers to let the user to vary the common look and feel of a web site (e.g. fonts, colors etc.) to give better accessibility or a more individual viewing experience.