To go along with its mobile interface revamp, Twitter has updated its universal Windows 10 app with a new personalization option for desktops and tablets. Like its mobile counterpart, the desktop version of Twitter now has its own dark theme.
To switch to the new dark theme, open Twitter, go to Settings and select Personalization, then pick "Dark" under the Theme options. You'll need to restart the app for the theme to change.
You can grab the updated version of Twitter for Windows 10 from the Windows Store now.