CSS

Cascading Style Sheets (CSS) is a language for describing the presentation of a document written in a markup language. CSS is designed primarily to enable the separation of document content from document presentation, including aspects such as the layout, colors, and fonts. This separation can enable multiple HTML pages to share formatting by specifying the relevant CSS in a separate .css file, and reduce complexity and repetition in the structural content. For each matching HTML element, it provides a list of formatting instructions.

Separation of formatting and content makes it possible to present the same markup page in different styles for different rendering methods, and can be used to display the document differently depending on the output screen size or device. Another Aesthetic changes to the graphic design of a document (or hundreds of documents) can be applied by editing a few lines in one file, rather than by a laborious and error-prone process of crawling over every document line by line, changing markup.