Prioritize Critical CSS

This filter first instruments the page to discover which CSS selectors will be used by the browser. It uses instrumentation results to select the critical CSS rules from the page and inlines those in <style> tags at the top of the document. It lazily loads the original CSS <style> and <link> tags after the page has loaded.

When you load this page, you may see one of several things:

If you see a flash of unstyled content as the page is loading, it is possible the beacon results that pagespeed collected did not include rules that apply to your browser.