Xiaomi
Change Contacts App Theme (Light or Dark) auf Xiaomi
The Contacts app on Xiaomi phones carries its own theme switch, separate from the phone-wide display mode set in system settings. That is why calls and messages screens sometimes stay light after you turn on dark mode for the rest of the interface, or the other way round.
To fix this, open Tap on Contacts ➔ Open the Menu ➔ Tap on Settings ➔ Tap on Theme ➔ Choose Light, Dark or System default. Picking System default links the app theme back to your phone-wide display mode, so it switches automatically together with your day and night settings or manual toggles.
Choosing Light or Dark instead locks the Contacts app to that look permanently, no matter what the rest of the phone does. This helps if you want calls and messages to always stay readable in bright sunlight, or always stay dim at night regardless of the system mode.
If the app does not update right away after changing this setting, force-close it and reopen it. If the look still does not match, check that MIUI dark mode itself is working correctly under the main display settings first.