macOS App to make specific apps Dark Mode?

Is there a macOS app that I can use to force specific apps into Dark Mode if they do not have a dark mode setting, like Messages. Messages will match the system scheme but I cant make it dark mode if the system is in Light Mode. I like to keep my apps on my secondary display in Dark Mode all the time.

Can you do the reverse?
Put the system in dark mode, and the apps on your primary display in light mode, overriding the system setting?

I only want to do it for one app. that way, I have to change every app that I open…