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.
If you count finger joints and tips, using your thumb – you can count in hex (base16) on each hand.