Cascading Style Sheets (CSS) is a style sheet
language used for describing the look and
formatting of a document written in a markup
language. While most often used to style web
pages and interfaces written in HTML and XHTML,
the language can be applied to any kind of XML
document, including plain XML, SVG and XUL.
CSS is designed primarily to enable the
separation of document content from document
presentation, including elements such as the
layout, colors, and fonts.[1] This separation
can improve content accessibility, provide more
flexibility and control in the specification of
presentation characteristics, enable multiple
pages to share formatting, and reduce complexity
and repetition in the structural content (such
as by allowing for tableless web design).
CSS can also allow the same markup page to be
presented in different styles for different
rendering methods, such as on-screen, in print,
by voice (when read out by a speech-based
browser or screen reader) and on Braille-based,
tactile devices. It can also be used to allow
the web page to display differently depending on
the screen size or device on which it is being
viewed. While the author of a document typically
links that document to a CSS file, readers can
use a different style sheet, perhaps one on
their own computer, to override the one the
author has specified. However if the author or
the reader did not link the document to a
specific style sheet the default style of the
browser will be applied.
CSS specifies a priority scheme to determine
which style rules apply if more than one rule
matches against a particular element. In this
so-called cascade, priorities or weights are
calculated and assigned to rules, so that the
results are predictable.
The CSS specifications are
maintained by the World Wide Web
Consortium (W3C). Internet media
type (MIME type) text/css is
registered for use with CSS by
RFC 2318 (March 1998), and they
also operate a free CSS
validation service.
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