I do something similar, but I just use a shell script:
https://github.com/theherk/commons/blob/main/bin/light-dark-..., and combine it with a raycast script to run it to run it:
https://github.com/theherk/commons/blob/main/rayscripts/ligh.... That takes care of it at a system level and for all my terminal configurations. Unfortunately, Firefox doesn't read its prefs file when written to, so that is a bit more difficult.