Following the November security update, the Pixel 3’s ‘Battery Saver’ feature forces the smartphone switch into Dark Mode.’
Oddly enough, it appears the phone will get confused if there are conflicting settings. Currently, on one of our in-office Pixel 3 smartphones, the Dark Mode setting will change depending on the wallpaper. Because of this, when I tap on Battery Saver, it changes my phone to Dark Mode. However, when I go back to the home screen, the device turns ‘Light Mode’ back on.
It appears, however, that this forced Dark Mode doesn’t change the theme of the App Drawer. Perhaps in a future update this functionality will change, though.
Google is making this change as the company recently noted how much Dark Mode can actually save battery life. Though it seems to only affect the ‘Settings Shade’ currently, likely with more updates, this battery savings shift should help save even more battery life.
Google also recently updated its Android’s stock Contacts app to feature Dark Mode.
Source: Android Police