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name: unused-css description: "Use when reviewing stylesheets, component styles, and responsive behavior related to Remove unused CSS rules. Check the rendered layout across breakpoints and interaction states before proposing a fix." metadata: category: css priority: high difficulty: intermediate estimatedTime: "25" source: frontendchecklist.io url: https://frontendchecklist.io/rules/css/unused-css

Remove unused CSS rules

Most projects use only 10-25% of their CSS—removing the rest can cut bundle sizes by 75%+ and dramatically improve load times.

Quick Reference

• Use PurgeCSS or UnCSS to remove unused selectors
• Integrate into build pipeline (Webpack, Vite, PostCSS)
• Safelist dynamic classes and framework-specific patterns
• Typical reduction: 50-90% for CSS framework users

Check

Use tools like PurgeCSS, UnCSS, or Chrome DevTools Coverage to identify and remove unused CSS to reduce bundle size and improve performance.

Fix

Implement automated unused CSS removal in your build process and regularly audit CSS files to eliminate dead code and unused selectors.

Explain

Explain how unused CSS bloats bundle sizes, slows page loading, and how modern tools can safely remove unused styles without breaking functionality.

Code Review

Review stylesheets, component styles, and responsive states related to Remove unused CSS rules. Flag exact selectors, declarations, or breakpoints that violate the rule in the rendered UI.

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For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/css/unused-css