Insightful post by the folks over at LogRocket on the rendering pipeline:
If your site takes forever to load, chances are your users aren’t gonna wait for it to finish, even if there’s valuable content to be found there. Some studies have shown that up to 50% of users leave a page after 3 seconds of waiting.
With users expecting those types of load times, it’s our responsibility as web developers to not bloat the amount of stuff we’re sending to the user. Sadly, CSS is often the culprit of increased load times, so having a nuanced understanding of how the CSS you send is transformed into beautiful pixels will help you optimize that crucial seconds where users are most likely to bounce.
How CSS works: Parsing & painting CSS in the critical rendering path →