The Autoptimize criticalcss.com Power-up has just been released to the wordpress.org plugin repository!
This plugin integrates with and extends Autoptimize. It integrates with criticalcss.com, a premium service which uses a “headless” browser to extract real critical CSS. That way it fully automates the extraction of high-quality critical CSS and the creation of rules for that critical CSS. It can work 100% automated, but also allows semi-automated jobs (where you enter a URL for which you want a specific rule, the power-up will do the rest) and manual rules (where you create the rule and add critical CSS yourself).