CSS needed to change selected text background color

[risk]

In the desktop app, how do I change the background color of selected text in the markdown editor?

There are a few posts about this same subject but the posts are either closed unanswered after 30 days or solutions provided for CSS to use in userechrome.css doesn't work.

Thank you in advance.

[personalizedrefriger]

Try

:root .CodeMirror-selected {
  background: red !important;
}

 

Note:
The default CSS, at least for my theme settings, is

.CodeMirror-selected {
    background: #6b6b6b !important;
}

[risk]

Thank you but sadly, neither snippet works.

[personalizedrefriger]

After selecting two lines, this is what the selection in the CodeMirror editor looks like for me in the development tools:

If these elements exist, does adding styles to these elements using the developer tools work? (For example, outline: 2px solid red;?)