u/Danrobi1

https://github.com/emacs-mirror/emacs/commit/d24b10ca75f49217f8585ce9c0fb53209693f882

Introduce 'margin' face for window margin background

A new basic face 'margin' is used for text displayed in the left and right margin areas, i.e., the areas typically used by VCS and LSP packages for per-line annotations. Its background defaults to the frame default, preserving existing behavior for users who do not customize it.