https://www.techradar.com/news/apple-announces-dark-mode-for-your-iphone

Apple has announced one of the most anticipated aspects of iOS 13 - Dark Mode. It's a setting that displays text and images against a dark background – perfect for night-time viewing or if you just want a more understated display.

When you toggle the setting on in the Control Center, the white and light gray display of standard iOS turns to black and dark gray, turning into a dark-side alternative.