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
font.
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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