I want to create a horizontal custom menu in wordpress. I've added a custom menu widget to the footer of my site (not online yet) but it displays a vertical bullet list menu. Where can I change that?

I'm using latest wordpress and the [Interio theme](http://themeforest.net/item/interio-responsive-multipurpose-wordpress-theme/4616897) if that helps any.

I don't know how to edit CSS for custom menu widgets. How do I do this?