There is a hidden feature that lets users turn on night mode for any iPhone app, or the closest thing to night mode. Apple lets users invert colors, which results in some weird colors in select apps, but makes it easier to use a web browser at night.
Go to Settings -> General -> Accessibility -> Invert Colors to On.
An easier way to turn this DIY night mode on and off is to set a triple click of the home button to invert colors. This won’t work with the other option to triple click for a home button, but this option may prove a better use for the triple click shortcut.