Hey David,
the submenus are styled by the code in the “Top Menus” section (line 278 and below) of the “style.css” file (located in the theme’s root folder); the styling is primarily executed via the “#nav-primary ul ul” declaration. In case you have some specific things you’d like to change about the submenus, you can give me more detailed information (and a URL of the page in question would also be useful), and I will help you with the code or at least try to provide a direction.
Sincerely,
Andrii / Satori Studio