interface - How can I reset this? - Blender Stack Exchange
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) :
Blender Themes | MeshLogic
2.79 Final Themes competition! - Blender and CG Discussions - Blender Artists Community
Call for Content: Themes - User Feedback - Developer Forum
Blender - Windows 98 Theme
Call for Content: Themes - User Feedback - Developer Forum
2.79 theme for 2.8 - Blender Stack Exchange
Call for Content: Themes - User Feedback - Blender Developer Talk | Toolbar icons, Blender 3d, New theme
Odyssey theme for 2.79 - Released Scripts and Themes - Blender Artists Community