Highlight active line number

What would be the best approach to setting the color of the active line only?

Could there be a case for a new CSS class to handle this also?
.CodeMirror-linenumber {color: #555; cursor: default}
.CodeMirror-linenumberactive {color: #0692b8}


Such a thing could be built rather easily by doing something like the activeline addon does, but adding a wrapper class, or the the recently added "gutter" class, instead of the background. Unfortunately, themes don’t currently specify any suitable styles for doing this in a cross-theme way.