How to Enable “Dark Mode”
iOS 11 introduces a display setting that inverts some but not all of the colors on your device. iOS has long had a setting to invert the colors on your device, but now it has a smarter invert option that leaves photos, videos and other elements alone. It’s the closest thing you’ll find to a dark mode for your iPhone or iPad.
Head to Settings > General > Accessibility > Display Accommodations > Invert Colors and toggle on Smart Invert. Watch the video as there is a lot to see.