CSS Non Blocking
Testing & Qualitycss-non-blockingCSS Non Blocking is an Agent Skill for testing & quality published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.
Use when reviewing stylesheets, component styles, and responsive behavior related to Load CSS without blocking render. Check the rendered layout across breakpoints and interaction states before proposing a fix.
How to use this skill
Bring this guide into your coding agent with a prompt tailored to the tool you use.
- Open your project in Codex.
- Copy and paste the prompt below.
- Review files and risks before approving any action.
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/css-non-blocking/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/css-non-blocking, but wait for my approval before writing files or running scripts.
Copying this prompt does not install or run the skill. Review third-party files before use.
Load CSS without blocking render
Render-blocking CSS delays First Contentful Paint—users see a blank screen while waiting for stylesheets to download and parse.
Quick Reference
- Use
<link rel="preload" as="style">with onload handler - Inline critical CSS, defer non-critical styles
- Use media queries to split CSS by viewport/feature
- Modern: Next.js/Vite handle this automatically
Check
Analyze this CSS loading implementation to ensure stylesheets are loaded without blocking the DOM parsing and rendering process.
Fix
Implement non-blocking CSS loading using the preload technique with media attributes and loadCSS polyfill for better performance.
Explain
Explain how non-blocking CSS loading improves page performance by preventing render-blocking resources from delaying the initial paint.
Code Review
Review stylesheets, component styles, and responsive states related to Load CSS without blocking render. Flag exact selectors, declarations, or breakpoints that violate the rule in the rendered UI.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/css/css-non-blocking