You'll need to use substratum for dark theme.
There's another option. You can use Andromeda (paid app) for rootless substratum on Oreo. You'll have to connect to a computer with ADB and run the Andromeda script. Then you can apply a theme from the substratum app. The Andromeda script has to be run each time you want to use a different theme.Thanks. Not looking to root the device but I appreciate it.
BlackBerry Launcher has a dark theme, no root required.Thanks. Not looking to root the device but I appreciate it.