A simple dark theme for sddm
$ git clone https://github.com/simonesestito/dark-arch-sddm
$ cd dark-arch-sddm
$ ./install.sh #Requires sudo authentication while installing
Then, apply the theme in KDE Settings (Settings > Workspace > Startup and shutdown > Login Screen (SDDM) > click on Simple Dark Theme, apply, authenticate and reboot)
Did you know? In install.sh you can easily select the logo you prefer. Isn't it in the list? Open an issue here on GitHub specifying the distro name and a url to the logo you want.