I chose the light theme on the mobile app for this forum. I find it very uncomfortable to read. the light theme is very dark, only a tiny bit lighter then the dark theme.
I don’t use the mobile app, but Chrome (on Android 9), and this is what I see with the Light theme:
Maybe there is an issue with the Discourse app.
this is the dark theme:
!
and this is the light theme:
I forgot I can take screenshots on the phone. Different generation 
it is slightly lighter then the dark theme, still not the brightest star in the sky.
@hex the light theme is supposed to be a white background and black text. I’m using it right now as I write this response in a desktop browser. Please try viewing the upstream discourse site itself to see if you can reproduce the behavior there.
Only the mobile application is affected.
I asked on discourse forum, I’ll post any insight here later.
Cause of this was system wide dark mode setting enabled on my device.