The responsive topbar uses Foundation 6 Responsive Navigation Patterns to make it easy to switch between accordion, dropdown and drilldown menus at different breakpoints.
To use this menu type, change the template part in header.php to:
<?php get_template_part( 'parts/nav', 'topbar' ); ?>
Responsive Menu Options
In the functions/menu.php file, locate the joints_top_nav() function. The two important lines of code are:
'menu_class' => 'vertical medium-horizontal menu', 'items_wrap' => '<ul id="%1$s" class="%2$s" data-responsive-menu="accordion medium-dropdown">%3$s</ul>',
Simply update the menu_class and items_wrap to match the navigation pattern you want. You also may need to adjust the class in functions/menu.php depending on the type of menu you are creating.