If you recall, Twitter's Android app gained a Night Mode feature last month. At that point, there was no information on whether or not the micro-blogging service's iOS app would be getting it. However now, it looks the feature may be coming to iOS as it's part of the latest beta build for the platform.
If you're a Twitter beta user on iOS, you'll be able to access the feature by heading to the app's settings menu - it's available as a new toggle option there. There's currently no information when the feature will be publicly launched, although given that it's already made it to the latest beta, that should happen sooner than later.