I would pay good money for this tool ~12 years ago. We had a site with enormous amounts of CSS that accumulated over the years and it was really unclear which rules are and which aren't critical
The mod_pagespeed filter "prioritize_critical_css" was released exactly 12 years ago in early May 2013. At least 3 more popular critical css tools were released the following year, integrating with Grunt, Gulp, and later Webpack.
