Developers are allowed to apply native themes for their app, or derive new ones throught inheritence. This decision has a significant impact on energy consumption since displaying dark colors is particularly beneficial for mobile devices with (AM)OLED screens. By default Android will set Holo to the Dark theme (parent style Theme.Holo) and hence switching to the light theme (parent style Theme.Holo.Light) within the manifest should be avoided. To a lesser extent, use of bitmap images with too high luminance should be avoided.
In order to support Dark theme (Android 9 and later), you must set your app's theme to inherit from a DayNight theme (parent style Theme.AppCompat.DayNight).