because the colors of connections (and soon, cards) are totally customizable, a traditional dark mode doesn't really work. e.g. you'll set your mode to dark and open someone else's space with colors designed around light mode.
The workaround , (that works pretty well tbh) is to set your space background to black #000. I also just launched the ability to set that to be your default for all new spaces you create (https://twitter.com/KinopioClub/status/1476569968414277634)