Allow lowering the volume too, not just increasing

Currently there is the “voice boost” which can increase the volume of the book separate from the system volume. I’d like to be able to adjust the volume down too.

My use case is that I’m usually playing white/pink noise while listening to a book when I’m trying to sleep. By being able to adjust the volume separately from the system volume I can make sure neither the narrator nor the white noise is too loud/quiet.

Currently this isn’t an urgent problem for me since I use Samsung which has a Sound Assistant app where I can set separate volumes for different apps, but other vendors might not have such apps.