# CSS Performance: What Slows a Page, and Critical CSS

See why a stylesheet holds up the first paint, find unused CSS with the Coverage panel, animate transform instead of layout, skip off-screen work with content-visibility, inline the critical CSS, and measure the result with Lighthouse.

![Cheat sheet: CSS Performance: What Slows a Page, and Critical CSS](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/10/b48c1281e3e942baa4a4e301a9a08eab.webp)

- Category: CSS
- Level: Freelancer
- Tags: Compositing, content-visibility, Critical CSS, CSS, Reflow, Repaint, web-development, will-change
- Updated: November 1, 2026

Source: https://www.ask-codey.com/cheat-sheets/css-performance-cheat-sheet