Lag from frequent style recalculations on profiles due to mouse and scroll position CSS variables

[khang06]

Describe the bug
Profiles start to get very laggy after scrolling down for a while. Some profiling shows that this happens due to the CSS variables introduced in #875 causing a full style recalculation after every mouse move/scroll input, which starts to scale really badly after scrolling through enough pages, even if the profile has no custom CSS! In one case, I had each style recalculation take as long as ~300ms.

Screenshots

Browser
Thorium 128.0.6613.189

Links
Should happen on any profile after scrolling enough, but the screenshot was from https://x.com/hourly_shitpost

OldTwitter version
v1.8.9.6

[dimdenGD]

I never seemed to have this problem, so if you can, you'll need to make a PR yourself so you'd be able to see if you fixed it or not

[khang06]

I never seemed to have this problem, so if you can, you'll need to make a PR yourself so you'd be able to see if you fixed it or not

It gets rid of the problem if I comment out the two event handlers on my local copy. Works for me since I don't care about custom CSS, but I don't think I should PR removing that feature for everyone. Maybe only registering the handlers if they're actually referenced in the CSS would be a good middle ground? It wouldn't completely solve the problem but I can't think of a way to implement this as-is without the eventual performance issues.