Inline Critical CSS and Async Load the Rest
Extract above-the-fold CSS into a style tag and load the rest asynchronously so the first paint does not wait for the full stylesheet.
Task
Apply <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> to reduce a measured bottleneck that shows up in the performance budget or Lighthouse audit.
When to use this
Lighthouse reports the page fails the performance budget because of <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'">, scoring 72 on mobile.
Prerequisites
- A Lighthouse or WebPageTest baseline measurement
- Access to the build configuration
Steps
1. Configure <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> in the project configuration file with the recommended defaults.
<style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'">
Expected output: The configuration is accepted and <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> runs without errors on the first invocation.
2. Run the check locally to verify <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> produces the expected result before pushing.
pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> blocks merge on failure.
- name: Run add critical css inline
run: pnpm test
Expected output: Pull requests with failing <style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'"> are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Measure before optimizing
Start by measuring the problem. Extract above-the-fold CSS into a style tag and load the rest asynchronously so the first paint does not wait for the full stylesheet. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run against the current codebase and inspect the output before wiring it into CI.
<style>/* critical */</style><link rel="preload" href="full.css" as="style" onload="this.rel='stylesheet'">Verify the improvement
Once the gate is in place, make failures actionable. A failing should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.