i made a blender theme i call "blackout" (i made this in 2.79, so i don't know if it will work in 2.91 but download link will be comming hopefully soon) :
Call for Content: Themes - Announcements - Developer Forum
Call for Content: Themes - Announcements - Developer Forum
GitHub - kame404/blender-themes: Modern themes for Blender 3.6 Alpha
Blender - Windows 98 Theme
Blend Swap | Blender Black-Red Theme - NanoTech
Softimage XSI MOD theme on Blender 2.8 – 3DCineTV
Blender Theme: Energy v18 - BlenderNation
Call for Content: Themes - Announcements - Developer Forum
Here's Blender 2.8 Theme for Blender 2.7 - Released Scripts and Themes - Blender Artists Community
blender-theme · GitHub Topics · GitHub
Maya 2018 Theme for Blender 2.79 - Released Scripts and Themes - Blender Artists Community