How to style autocomplete/hint dialog boxes?

I have followed CodeMirror Autocompletion Example, now I would like to style the dialog boxes, any hints? I can style the dialog boxes with some prefixed ids from CM, but whats the proper way, or a way in which I can create my own names for the boxes.

Yes, that’s the idea, target classes with a cm- prefix with custom rules, possibly from a theme extension for convenience.