Hi,
That list actually comes directly from Google so it uses their classes.
You can use Firebug or the IE developer tools to ‘inspect’ the list and see which classes and styles are being used.
I think the list is in a div with class ‘adp-list’. You can style it from there.
As an example, MapPress puts a border around the list – this is from ‘mappress.css’ in the plugin directory:
.adp-list { border: 1px solid lightgray ; cursor: pointer ; }