Welcome to Slippi-HUD, a nodecg package that can be used to power all kinds of slippi powered melee streams. You can create your own custom HUD, or an auto updating stream overlay.
I'm a madman, obviously
And? All you have to do is make your own html/css, the source code is right here.
The Debug template contains the answers you seek.
Node, Javascript, and Lit as I understand.