For my sins I occasionally create large PRs (> 1,000 files) in GitHub, and teammates (who mostly all use Chrome) will sometimes say "I'll approve once it loads for me..."
But CSS has bit me with heavy pages (causing a few seconds of lag that even devtools debugging/logging didn't point towards). We know wildcard selectors can impact performance, but in my case there were many open ended selectors like `:not(.what) .ever` where the `:not()` not being attached to anything made it act like a wildcard with conditions. Using `:has()` will do the same with additional overhead. Safari was the worst at handling large pages and these types of selectors and I noticed more sluggishness 2-3 years ago.
Normally, you be able to debug selector matching performance (and in general, see how much style computation costs you), so it's a bit weird if you have phantom multi-second delays.