Need help with creating menu, that unfolds on hover and sticks to the top

Hey guys. I asked already in support if it is possible to do a menu, that unfolds on hover and sticks to the top like the one that COS has https://www.cos.com/de_de/index.html
But they told me with widgets it is not possible, so maybe some custom code can work. Let me know, please, if you have any ideas, how to make it.

Huge thanks,
Anastasia