In order to keep your header fluid, you can pick a menu from the created menus in your wordpress.
If you check this option, the menu will be invisible and a toggle button will appear instead of the full menu.
You can choose to add search to your menu or not.
This options allow you to stop the responsive style for the menu on small devices and render the menu in it’s default state ( just text without a toggle button ).
Recommended in case you have 2 or three menu items.