Styling the outline of a merge view editor

I am trying to add an outline to a merge side. It works fine in a standalone EditorView, but when part of a MergeView as side a or b, it doesn’t get applied for some reason. Here is an example:

Merge view with outline on focus using theme styling

(I realize that a standalone EditorView does not work on Try CodeMirror website either, it works on my machine; so I cannot provide a working example)

Thank you in advance,

Themes passed to CodeMirror are scoped to the editor itself, so you’ll have to use raw CSS to style the .cm-mergeView element around them.