Pretty much every app now has one, and TikTok is also now jumping aboard the 'dark mode' train, with a new setting for low light situations now available to some users.
TikTok is about to launch its own Dark Mode option pic.twitter.com/JSgQVbzsGh
— Matt Navarra (@MattNavarra) January 28, 2020
As you can see in this tweet from social media expert Matt Navarra, the new dark mode option will either seek to match your device settings, when you have dark mode activated, or you'll be able to manually switch to dark mode in your app settings.

Dark mode options lessen the impacts of blue light exposure, which can, in some cases, cause your brain to stop producing melatonin, and disrupt your sleep cycle. That then leads to other health impacts - so aside from giving your app a new look, dark modes actually do serve an important health purpose.
But TikTok's variation does also look kind of cool. If you don't see the option in your version of the app, it's likely rolling out sometime soon.