And in a moment you’ll learn, that at your scale, for the practical purposes, the universe rounds pi to n numbers. E.g. ~3.1416. Check & mate.

interesting to code, but totaly useless shit

Easyest way, to begin with, is to use a browser addon and userscripts. Addons to look for are Greasemonkey, Tampermonkey, or Violentmonkey and alike alternatives. Keyword to google “userscripts”. P.S. As I see it, from your description, you just want some mods (changes) to existing UI, no need to rebuild one from a scratch in other more complicated ways.

That’s your chance to turn away from rpm/RHEL distros and run without looking back. As last 20 years history shows, that branch of linux OS is either dying off on hands, leaving you without suport, either makes migration path complicated by a need to change distro. Like it was with centos +5…10 years, oh no … -> maybe fedora -> oh no … -> whatever whocares rpm pop/rocky/alma name it … Thats it, beat it, no more this shit.

deb or any other kind linux is a way to go.