Render blocking

Lighthouse treats a script in the head without defer or async, and a stylesheet without a disabled attribute or a non-matching media query, as render-blocking: first paint waits until they are downloaded and parsed. Inlining critical CSS and JavaScript, deferring the rest (defer/async, asynchronous stylesheet loading) and removing unused code shorten the delay. Where supported, Resource Timing's renderBlockingStatus reports which resources blocked; the property is not available in all major browsers.