Theme background colors override selection styling

I’m working on a theme that sets a background color for strings and finding it difficult to edit text when it’s active. The problem is that the selection highlight is drawn behind the background color from the theme, so the selection is invisible inside a region that’s highlighted with a background color. This is surprising, since I think most editors that support background color syntax highlighting will draw selections on top of the highlighting.

Is there any way to control this from within the theme or, if not, could the default behavior in Nova be changed?