GLOSSARY TERM
What is Critical CSS?
Definition
The minimum CSS required to render above-the-fold content, inlined directly into the HTML head to avoid blocking render on an external stylesheet request.
Why it Matters for AI Search
Inlining critical CSS shaves 100-300ms off FCP for most sites. Tools like Critters or PurgeCSS can automate the extraction. The trade-off is HTML payload size — keep it under 14KB to stay within the initial TCP packet.
Related Terms
Render-Blocking ResourcesLCP (Largest Contentful Paint)Lazy LoadingHTTP/3Meta Robots TagFCP (First Contentful Paint)
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