What is CSS?

Tomasz Bogusz

CSS, Cascading Style Sheets, is a computer style sheet language that controls the visual aspects of computer documents. A collection of stylistic rules through which CSS controls those aspects is called a style sheet.

CSS was first proposed in 1994 by Håkon Wium Lie who at the time was working with the creator of HTML, Tim Berners-Lee, at CERN. CSS was an extension of ideas of other style sheet languages that already existed in the 1980s and were dedicated to styling documents written in congruence with SGML (Standard Generalized Markup Language) standard.

CSS can be used to style in particular:

  • HTML documents,

  • XML documents, and

  • Scalable Vector Graphics (SVG) elements.

CSS, just like other typical style sheet languages, controls the visual aspects of supported computer documents through its set of stylistic rules that can be divided into:

  • property rules - governing the application of visual aspects to a given document element through the usage of properties,

  • selecting rules - governing the selecting of elements to which property rules should apply,

  • inheritance rules - governing the way in which property rules applicable to elements are inherited by (cascade to) their children elements.