How to run an app in dark mode without changing Linux's global system settings

Using a Linux distro with Gnome desktop and want to run a specific app in dark mode, without having to change your entire system’s theme setting?

Here you go:

$ GTK_THEME=Adwaita:dark <app-name>

You can replace Adwaita:dark with any other available theme. To find your available themes you can inspect your themes folder:

$ ls /usr/share/themes/
Adwaita       Emacs         Pop-dark       Pop-light-slim  Pop-slim-light
Adwaita-dark  HighContrast  Pop-dark-slim  Pop-slim        Raleigh
Default       Pop           Pop-light      Pop-slim-dark