Critical CSS and render-blocking resources
type: TechArticle
description: Inline the CSS needed for above-the-fold content and defer the rest. Render-blocking resources in are the single biggest cause of slow first paint.
language: en
is part of: Web Specification Studio
author: Web Specification Studio
publisher: Web Specification Studio
license: https://creativecommons.org/licenses/by/4.0/
date modified: 2026-05-29T09:13:20.000Z
citation: web.dev — Extract critical CSS
  type: CreativeWork
  publisher: web.dev
citation: web.dev — Defer non-critical CSS
  type: CreativeWork
  publisher: web.dev
citation: MDN — Render-blocking resources
  type: CreativeWork
  publisher: MDN
citation: Chrome for Developers — Eliminate render-blocking resources
  type: CreativeWork
  publisher: Google

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breadcrumb
type: BreadcrumbList
item list element: Home
  type: ListItem
  position: 1
  item: https://webspecification.com/
item list element: Spec
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  position: 2
  item: https://webspecification.com/spec/
item list element: Performance
  type: ListItem
  position: 3
  item: https://webspecification.com/spec/performance/
item list element: Critical CSS and render-blocking resources
  type: ListItem
  position: 4
  item: https://webspecification.com/spec/performance/critical-css/