Sensible course of action ...
In the meantime I edit the styles on my subdomain, not via a copy like you. Your idea is good, but the members can select and activate your fumble design in the profile. and watch what you do :-)
I'm currently in the process of recreating the design of the Euro Truck Simulator 2 in-game menu. And so that my people can't watch, I do that on the subdomain ;-) and the DarkCore style is ideal for this ... ;-)
EDIT; Take a look at the screenshot, I'm concerned with the frames, the icons are irrelevant ... the frames and colors are important to me.
I don't yet know exactly how I will implement this, I probably have to change something in the templates or work with: before: and: after: ... maybe @RobiNN also has a few tips