[Hugsbox]

This is extremely laggy on my computer. It may not be a top-end gaming supercomputer but it's no slouch either.

[esperent]

It's fine on my phone, Brave Android. Maybe it doesn't work on Firefox?

[sheept]

It might be related to the liquid glass imitation in the color scheme picker

[bduffany]

I think you're right. Performance profile shows lots of long spans relating to that element, and deleting that element makes the page scroll much more smoothly.

There are still other issues though. The performance of this page feels pretty bad in general.