Give me some tips for how to I enable iOS 11's hidden dark mode?
It is very simple to enable IOS 11's hidden dark mode, just follow these steps:
Open Settings on your iPhone.
Head over to General > Accessibility > Display Accommodations > Invert Colors and turn on Smart Invert. Your eyes should thank you now.
You may try this Toggle ON Invert Colors (Settings > General > Accessibility > Display Accommodations).