The native dark mode in the latest MIUI 10 beta covers most areas of the operating system — Phone, Contacts, Gallery, Screen recorder, Updater, Messaging — as well as the notification shade, volume slider, and the Recents menu. Xiaomi confirmed a month ago that MIUI 11 is in the works, so the stable MIUI 10 with dark mode should come out soon.
https://www.notebookcheck.net/MIUI-10-beta-comes-with-native-dark-mode.407826.0.html