How do I put Facebook into dark mode on iPhone?

Lots of apps have a dark or night mode to make viewing in low light environments easier on the eye, how do I turn on Facebook's dark mode?

Update: Facebook added an official Dark Mode feature to the Facebook iOS app. Click here to see how to enable Facebook Dark Mode on iPhone.

How to activate Dark Mode on Facebook Messenger

While many apps like YouTube, Twitter and Reddit have their own dark modes for low light viewing, Facebook does not. Instead, Facebook has optimized its app to work with iOS's Smart Invert Colors feature, which is essentially a dark mode. Follow these instructions to turn on Smart Invert Colors on your iPhone or iPad.

How to turn on dark mode on Facebook on iPhone and iPad.