Pretty much all graphical apps that dont have thier own theming option (like firefox) are always just the white background default theme. No matter wether it’s qt or gtk. Wich files would i need to edit to change that? Searching on the internet only told me that i should change an environment variable bit doing so changed nothing even though i have the themes installed
I would figure out your environment variables first. It’s likely based on what you’re saying that your setting those variables only for interactive shell and not someplace where they are sourced by your WM or whatever is launching your WM.
Check out this section of the ArchWiki article. The rest of the article may also have some useful info.