Per T193210#4164456 I think what might be desired here is to set the colour of free-flowing text that is not nested in something.

So here "foo" should be given the specified colour, but not "bar":

Foo [[Main Page|bar]]

== Bar ==
Foo

If this is the case .CodeMirror-lines won't work.

For line height however, setting the line-height property on .CodeMirror-lines should work.

@Doc_James @Wbm1058 — There is currently no way to customize 'normal' text (such as figs on this example.) You can change the font weight of all text inside the CodeMirror surface, which may address your concern. If this is still a problem, we can create a new ticket in the MediaWiki-extensions-CodeMirror backlog.

And one friendly word or warning: change the line height at your own risk, we've seem some corner-case defects on some browsers where line height caused some blurry text. We hope it works alright for your browsers of choice!

I added a note about .CodeMirror-lines in the documentation. There is a disclaimer that this should be used "at your own risk". Many things will work fine but indeed changing the line-height will only reliably work in older wikitext editors. I should say the same is true for all of the available CSS classes, though. So really all I've done is document that .CodeMirror-lines exists.