[Neos] Main Menu

[Jean Claude]

hello ...
I wish to make a menu with a submenu.

with demo TYPO3.NeosDemoTypo3Org, there is the main menu with SecondLevelMenu appears horizontally below the main menu with such "features" ...
Instead I wish it SecondLevelMenu appears with a click of a dropdown menu as in the examples of Boostrap.
I understood for the css, but I can not find how to do it in the wrap Default.html page ...

if you could put me on the track ... it would allow me to continue my lurning with neos ...
in advance, thank you
jean-claude