For me in both Windows Chrome and iPad Chrome, dark mode for prepubs is only applied to the bottom bar not to the main text frame.

I can’t help you there, because I’m using the JNC’s iOS app on my iPad Pro, but I’ve used the dark mode in the app in the past.

Edit: I went to the JNC release calendar to select a prepub part for reading in Safari, and the “dark” option in the reader settings gives me white text on black background for the latest Land Mines v13 prepub part.

I also don't see a dark mode setting for the forums, and it doesn't happen automatically with the OS and browser set to dark mode.

For the reading the forums, I use the “superhero” skin in the settings, but it doesn’t apply to writing posts (I’ve got black letters on white background as I type).