It looks like Discourse have been making some more fancy improvements to having a dark mode/theme, that should be very easy to bring over to here.
The first is a button to toggle the theme between light and dark mode that sits in the bottom left-ish part of the screen. This is a big improvement as it greatly simplifies the process, over having to go into your interface settings to switch the theme that way.
The other is to have the dark mode colour scheme automatically switch based on the users' device. On PC for both Windows and Linux there exists third party programs that can switch the UI colour scheme from light to dark depending on the time of day, along with on Android and iOS.
Now there just needs to add an automatic theme switcher to OpenWrt itself. 