How to create mobile menu?
To create mobile-menu you have to add dropdown-menu class to menu that you want to be shown on small-screen devices. For this menu to work correctly you might want to add several other classes, such as icon-menu, show-small, hide-big (should be added without commas). Note that all of these classes including dropdown-menu should be added only to 1-st level item of your mobile menu.
Perhaps, the image below may better describe the desired structure of mobile-menu.
(Higher Resolution Image)