Render-Blocking CSS

Large CSS files in the head blocking first paint.

Medium priority · Core Web Vitals

What it is

Synchronous, unminified CSS in the <head> blocks rendering until downloaded and parsed, delaying first paint and LCP.

Why it matters

Render-blocking CSS is a leading cause of slow first paint, especially on mobile, and drags Core Web Vitals scores down.

How to fix it

Inline critical CSS, defer or preload the rest, remove unused CSS, split bundles per route, and minify. Audit with Lighthouse coverage.

What our AI checks

Our engine flags pages with slow starts tied to CSS and recommends inlining and deferral strategies.

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