What is Critical CSS?
The short answer
Critical CSS is the minimal set of styles needed to render the first visible part of a page, inlined in the HTML so the page can draw immediately.
Critical CSS, explained
The rest of the stylesheet loads without blocking. Many frameworks handle this automatically.
Questions people ask about Critical CSS
What is Critical CSS?
Critical CSS is the minimal set of styles needed to render the first visible part of a page, inlined in the HTML so the page can draw immediately.
Related terms
Render-blocking resources are stylesheets and scripts the browser must download and process before it can draw the page, delaying the first paint.
First Contentful PaintFirst Contentful Paint is the moment the browser first draws any text or image from the page, the first sign to a visitor that something is happening.
Page speedPage speed is how quickly a web page loads and becomes usable, measured by metrics like Largest Contentful Paint, Interaction to Next Paint and layout stability.
Core Web VitalsCore Web Vitals are Google's three user-experience metrics: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness and Cumulative Layout Shift for visual stability.
Part of the Web Encyclopedia by Apex Flow Digital. Definitions are general knowledge, kept current, with no invented statistics.