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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.
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CSS is designed
primarily to enable the
separation of document content
from document presentation,
including elements such as the layout, colors,
and fonts. 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-calledcascade,
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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