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CSS stands for Cascading Style Sheets. It is a language that describes how structured documents such as web pages should look and render across different media, including screens and print. HTML or XML provides the document’s structure and meaning; CSS supplies presentation rules that a browser or other user agent applies.
What does CSS mean?
CSS is short for Cascading Style Sheets. The World Wide Web Consortium (W3C) defines CSS as a language for writing style sheets that describe the rendering of structured documents such as HTML and XML across a variety of media. The W3C CSS Snapshot 2026 was published as a Group Note on 22 June 2026.
In practical terms, a style sheet contains rules that tell a browser how to present matching elements—for example, what color text should be or how much space should appear around a section. CSS can describe presentation for screens, paper, speech, and other media. MDN’s CSS overview offers a beginner-oriented introduction.
What is CSS used for?
CSS controls presentation: it can set visual properties such as color, typography, spacing, and layout for elements in a document. It generally does not change the underlying semantics or structure expressed by HTML or XML. A heading remains a heading in the source document even when CSS changes its appearance.
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This separation lets the document language express what content is, while styles describe how that content is rendered. The browser interprets the source document and its applicable style rules together.
How do CSS rules work?
A CSS rule uses a selector to identify elements and a declaration block to set one or more property-value pairs. For instance, a rule might select all paragraphs and set their text color. The browser checks which rules apply to each element and determines the resulting values.
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More than one applicable rule can set the same property on the same element. The cascade is the conflict-resolution process that determines which declaration wins. MDN explains the cascade as a sequence of checks:
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minute- Relevance: The browser filters out declarations whose conditions do not apply.
- Origin and importance: It compares where declarations come from and whether they are marked important.
- Specificity: If declarations remain in conflict, the browser compares how specifically their selectors target the element.
- Scoping proximity: Where relevant, it considers how close a declaration is to the element in its scope.
- Order of appearance: If earlier criteria tie, a later declaration in the source order takes precedence.
Because these checks are ordered, specificity is not the only factor—and source order does not automatically override every other rule. The cascade considers earlier criteria first.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is CSS one single standard such as CSS3?
Modern CSS is modular: its features are specified and progress in separate modules rather than as one unified release called CSS3 or CSS4. Module names may have their own levels. The W3C publishes snapshots that collect specifications the CSS Working Group considers stable enough to include.
The W3C says its 2026 snapshot reflects specification stability, not browser adoption. A feature’s inclusion in the snapshot therefore does not prove that every browser supports it. Check the support information for a particular feature before relying on it in a project.
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