Not debouncing the scroll action seems like a pretty poor idea. This could use some optimization for sure. Also, not hugely important, but my OCD hates that the

Not debouncing the scroll action seems like a pretty poor idea. This could use some optimization for sure. Also, not hugely important, but my OCD hates that the source code has several misspellings and inconsistent use of const/var/let. A little confused why you're using useCapture = true in the addEventListener call. Neat CSS, I learned a couple things.