Style of the menue

Hi there! I need help styling the menue. Usually I do WP-Homepages, this time I tried Blocs (since my client won’t do any changes anyway).
I’m having a hard time changing the apperance of the menue.
I tried giving the menue a class and styled normale, hoover and active, but whenver I preview it, it has just the default apperance (blue).
Can anyone guide me into the right direction to achive a menue like this?

Is this a mobile view of the menu?

You can style the menu appearance through the css manager. Just click on plus and the submenu will be opened.