Cascading Style Sheets (CSS) are a form of language that give a web page its look and feel. More generally, they can be applied to any document written in a markup language. One example of markup languages is Hyper Text Markup Language, or HTML.

Documents are specified a particular style – font, text formatting, background color, font color – essentially whatever elements are integral to the overall look of the site. The conformity of each page with the next gives an overall impression of style to the whole site. It is also a great method of building web pages, as the same style can be applied in each case without being applied in each case individually. This saves time in webmastering and development.

CSS also has other great functionality – a page can be rendered differently in different media. A page can be rendered to fit a cell phone window, or omit unnecessary content that would be costly in ink use when the page is printed from the Web. So it may look different on the printed page to in a browser window. There are other media that can exploit cascading style sheets, such as Alt text. Alt text may appear when an image is hovered over, for example, or captioning for images themselves may appear for a similar result. This is integral in media that exploit software for those who may not otherwise appreciate the image. Speech recognition software, Braille, and tactile applications for the visually or hearing impaired often employ some kind of CSS formatting.

Formatting can be overridden by a viewer’s browser: So if a user is not happy with the style that he is subjected to by a designer, he or she can use their browser’s default or specified settings to return to the look and feel to which he is accustomed.