Swift Black Substratum Theme
is a new app for Android that allows you to apply dark mode to apps on your phone that otherwise don't offer that feature. Using dark mode is know to help preserve your battery performance and reduce the strain on your eyes.
The app offers over 200 professionally edited overlays that convert your favorite apps into dark mode while maintaining quality and color schemes. You will most likely need to root your device and upgrade your firmware in order to use Swift Black Substratum Theme, and you can find details on the Google Play download page