Twitter is reportedly testing an alpha version (5.112.0-alpha.423), given to selected testers whcich has a feature of Dark UI. The current version of Twitter App for Android has a white background. The latest alpha update has an automatically enabled night mode dark UI, while time goes to the night in the correspondent timezone.
The dark theme is of Darker Blue-Black color with white characters and blue elements. There is no manual switching or enable/disable option in this alpha version. We could expect it with the final stable version.
Apart from the Dark UI Mode, twitter also introduced some UI changes like side slide menu and floating action buttons. Also a “Connect” feature seen in new APK from APKMirror. The new changes will make easier handling of twitter handles via smartphone and will give you a strain less vision, while you are using it in dark rooms.