CSS Coverage and Unused Styles
Identify and remove unused CSS using DevTools Coverage panel and tree-shaking tools like PurgeCSS.
The Unused CSS Problem
Large CSS files often contain styles for components not present on the current page. Every unused byte increases parse time, CSSOM construction time, and transfer size. A typical production app may have 90% or more unused CSS on any given page.
Chrome DevTools Coverage
Open DevTools → Coverage panel (Cmd+Shift+P → Coverage). Start recording, interact with the page, then stop. The panel shows each CSS file with percentage used and highlights unused rules in red. Export coverage data as JSON for analysis.
All lessons in this course
- Critical CSS and Render Blocking
- Layout Paint and Composite: The Rendering Pipeline
- will-change and Layer Promotion
- CSS Coverage and Unused Styles