I can't seem to be able to get a proper dark mode working for Kate.
The system is in dark mode, as configured in Settings -> Appearance -> Style.
In Kate, the default color scheme is Breeze Dark, the editor part itself is in dark mode but not the rest.
Installing breeze and reopening Kate yielded no different results.
sudo apt-get update
sudo apt-get install -y breeze
Ubuntu 22.04 LTS, Kate version 21.12.3
EDIT: After a system update the issue has seem to resolved itself, changing the color scheme now changes all the colors. I suppose if someone has a "proper fix" they can chime in.