Tried a a couple of dark themes developed for EMUI 9.0 / 9.1 , quite buggy oln Magic 2.1.0, but at the end I think I found one quite compatible and looking great (just changed the wallpaper):
(Edited)Deep Black by Maurydes
Nearly perfect so far, only the 3 navigation keys/icons at the bottom in some situations are not really good visible, but then again, I am not that young anymore, needing reading glasses.
BY THE WAY, I'm not using the stock launcher, whatever it's called...
I go with - Nova P rime launcher - all the way and all the time, since many years ago...
EDIT 4 aug. 2019
Another way , easier...
Just go to the Play store and run it.
Not exactly the same dark theme I had, but it's as nice and dark as... https://play.google.com/store/apps/d....com.gpix2dark
Also, try this
Third party theme app to push various themes: https://play.google.com/store/apps/d...emanager&hl=en
And follow the instructions to the letter.
The other theme I mentioned - DEEP BLACK V2 from Maurydes, you will find it also here : https://forum.xda-developers.com/mat...theme-t3877187
And all kudos to him ..