CSS (Cascading Style Sheets)

aid: css
x-type: concept
deliveryModel:
  model: unknown
  open_source: unknown
  commercial: false
  callable_host: false
  label: Delivery model not determined — needs a product licence on record
  confidence: low
  source:
  - repository-unlicensed
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source: []
  generated: '2026-07-22'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/css.png
url: https://raw.githubusercontent.com/api-evangelist/css/refs/heads/main/apis.yml
kind: standard
name: CSS (Cascading Style Sheets)
description: Cascading Style Sheets (CSS) is a W3C web standard for describing the presentation of documents written in HTML
  and XML, including layout, colors, typography, and animations. CSS is a foundational web technology defined by the W3C CSS
  Working Group and is implemented natively by every major web browser. The CSS Object Model (CSSOM) and CSS Houdini extensibility
  APIs expose CSS to JavaScript at runtime.
tags:
- CSS
- Web Standards
- W3C
- Styling
- Browser
- Specification
- Validation
- CSSOM
- Houdini
- Frontend
tags_raw:
- CSS
- Web Standards
- W3C
- Styling
- Browser
- Specifications
- Validation
- CSSOM
- Houdini
- Front End
specificationVersion: '0.23'
created: '2025-01-01'
modified: '2026-09-07'
apis:
- name: W3C CSS Validation Service
  description: The W3C's public CSS validator, exposed as a web service. A single safe operation checks a stylesheet — supplied
    either as a URL or as inline text — against a chosen CSS profile and returns the errors and warnings found, in XHTML,
    plain text, SOAP 1.2 or JSON. It is anonymous and free, and W3C publishes a WSDL 2.0 description of the SOAP interface.
    This is the only callable HTTP surface associated with CSS; CSS itself is a specification, not a hosted service.
  humanURL: https://jigsaw.w3.org/css-validator/
  baseURL: https://jigsaw.w3.org/css-validator/validator
  image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/css.png
  tags:
  - CSS
  - Validation
  - Conformance
  - W3C
  - SOAP
  properties:
  - type: WSDL
    name: CSS Validator WSDL 2.0 description
    url: wsdl/css-validator.wsdl
  - type: Documentation
    name: CSS Validator documentation
    url: https://jigsaw.w3.org/css-validator/documentation.html
  - type: APIReference
    name: CSS Validator Web Service API
    url: https://jigsaw.w3.org/css-validator/api.html
  - type: GettingStarted
    name: CSS Validator User Manual
    url: https://jigsaw.w3.org/css-validator/manual.html
  - type: Authentication
    name: Authentication profile
    url: authentication/css-authentication.yml
  - type: RateLimits
    name: Published rate limits
    url: rate-limits/css-rate-limits.yml
  - type: Conventions
    name: API conventions
    url: conventions/css-conventions.yml
  - type: ErrorCatalog
    name: Fault and finding catalog
    url: errors/css-problem-types.yml
  - type: DataModel
    name: Validation response data model
    url: data-model/css-data-model.yml
  - type: Sandbox
    name: Public validation console
    url: sandbox/css-sandbox.yml
  - type: CLI
    name: css-validator command line
    url: cli/css-cli.yml
  - type: SourceCode
    name: w3c/css-validator
    url: https://github.com/w3c/css-validator
features:
- name: Cascading and Inheritance
  description: Cascade, specificity, and inheritance rules combine author, user, and UA stylesheets.
- name: Selectors
  description: Selectors Level 3/4 match elements by tag, class, id, attribute, structure, and state.
- name: Box Model and Layout
  description: Block, inline, flex (Flexbox), and grid layout systems for composing pages.
- name: Responsive Design
  description: Media Queries Level 3/4 enable layouts that adapt to viewport, capability, and user preferences.
- name: Color and Typography
  description: CSS Color Levels 3-5 and CSS Fonts Level 3-4 define color spaces, gradients, and font features.
- name: Animation and Transitions
  description: Keyframe animations, transitions, and motion paths driven entirely from stylesheets.
- name: CSSOM
  description: The CSS Object Model exposes CSS rules and computed styles to JavaScript via DOM APIs.
- name: CSS Houdini
  description: Low-level browser extensibility APIs (Paint, Layout, Properties and Values, Animation Worklet) for custom CSS
    behaviors.
useCases:
- name: Web Page Styling
  description: Authors style HTML documents using stylesheets shipped with their site.
- name: Responsive and Adaptive UI
  description: Apps adapt presentation to device, viewport, and user preferences (dark mode, reduced motion).
- name: Component Libraries
  description: Design systems publish CSS-based components consumed by many applications.
- name: Web Animations
  description: Marketing sites and apps animate UI states purely with CSS.
- name: Browser Polyfills
  description: Houdini Paint and Layout worklets polyfill new CSS features in older browsers.
- name: Accessibility
  description: Authors honor user preferences (prefers-reduced-motion, prefers-contrast) via media features.
common:
- type: DomainSecurity
  url: security/css-domain-security.yml
- url: https://www.w3.org/Style/CSS/
  name: CSS at W3C
  type: Website
- url: https://www.w3.org/TR/?tag=css
  name: CSS Specifications (W3C TR)
  type: Specification
- url: https://www.w3.org/Style/CSS/current-work
  name: CSS Current Work
  type: Documentation
- url: https://www.w3.org/groups/wg/css/
  name: CSS Working Group
  type: Community
- url: https://github.com/w3c/csswg-drafts
  name: CSSWG Drafts (GitHub)
  type: GitHubRepository
- url: https://github.com/w3c/css-houdini-drafts
  name: CSS Houdini Drafts (GitHub)
  type: GitHubRepository
- url: https://www.w3.org/TR/CSS22/
  name: CSS 2.2 Specification
  type: Specification
- url: https://drafts.csswg.org/
  name: CSS Editor's Drafts
  type: Specification
- url: https://developer.mozilla.org/en-US/docs/Web/CSS
  name: MDN CSS Reference
  type: Reference
- url: https://www.w3.org/Style/CSS/
  name: CSS at W3C — developer portal
  type: DeveloperPortal
- url: https://www.w3.org/Style/CSS/learning
  name: Learning CSS
  type: GettingStarted
- url: https://www.w3.org/Style/CSS/current-work
  name: CSS Current Work — what is being worked on and what is next
  type: Roadmap
- url: https://www.w3.org/blog/CSS/
  name: CSS WG Blog
  type: Blog
- url: https://github.com/w3c
  name: W3C on GitHub
  type: GitHubOrganization
- url: https://lists.w3.org/Archives/Public/www-style/
  name: www-style public mailing list
  type: Support
- url: https://status.w3.org/
  name: W3C Status
  type: StatusPage
- url: https://www.w3.org/policies/process/#rec-rescind
  name: W3C Process — superseding, obsoleting and rescinding a Recommendation
  type: Deprecation
- url: https://www.w3.org/policies/
  name: W3C Policies and Legal Information
  type: TermsOfService
- url: https://www.w3.org/policies/privacy/
  name: W3C Privacy Policy
  type: PrivacyPolicy
- url: https://www.w3.org/Style/CSS/Test/
  name: Official W3C CSS Test Suites
  type: Tools
- type: Vocabulary
  name: CSS properties and descriptors
  url: vocabulary/css-vocabulary.yml
- type: Packages
  name: W3C-published CSS packages
  url: packages/css-packages.yml
- type: LLMsTxt
  name: llms.txt
  url: llms/css-llms.txt
- type: Lifecycle
  name: Specification and service lifecycle
  url: lifecycle/css-lifecycle.yml
- type: ChangeLog
  name: CSS Snapshots and validator releases
  url: changelog/css-changelog.yml
- type: Conformance
  name: Conformance and domain standards
  url: conformance/css-conformance.yml
- type: Plans
  name: Cost model
  url: plans/css-plans-pricing.yml
- type: AgentSkill
  name: Agent skills
  url: skills/_index.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
x-enrichment:
  date: '2026-09-07'
  status: enriched
  artifacts_added: 20
  pass: local-v3