Refactor JavaScript

I'm working on this

This is ready for review. Note I'd like to get this in ASAP, as any further JS work will conflict with this.

I've tested it and it works the same as it did, so no bugs introduced. Plus the code looks good. I'd rather merge this and work on top of that for any further change. Thanks Mike!

I would also manage black hover text with floating UI here.
Because now when we put submenu to fixed position it works fine with sidebar overflow: hidden
But that black text is not

@finnsky I'd keep improvements to smaller follow-ups to avoid conflicts, and leave this to a refactor :)

mherchel → credited claireristow → .

Committed dbba902c

Automatically closed - issue fixed for 2 weeks with no activity.