Rendering in Fractions of a Second

Users hate waiting. If your CSS file weighs 500KB, the browser will wait for it to load before showing the site. Critical CSS solves this problem.

The Method:

You determine styles needed to render the first screen (what the user sees immediately, without scrolling).
You insert this CSS directly into HTML via the <style> tag in <head>.
The main heavy stylesheet loads asynchronously in the background.

Result:

User sees the header and title instantly. While they start reading, the remaining styles load.

Tip

For automatic " critical CSS " extraction, there are special tools like Penthouse or PostCSS plugins.

Important

The Critical CSS method is critically important for SEO (LCP metric in Core Web Vitals) and mobile conversion.