Top menu behaviour

Hello all,

I need some guidance. I would like to make top menu open all sub-menus on hover, like it is done on this website:
http://inzinerijoslicejus.ktu.edu/

Could anyone tell what I need to achieve it? CSS? JQuery?
Perhaps where is a plugin with same effect?

I searched for menu plugins and best of what I could find was mega menu’s, which are awesome, but not exactly what I need.

Best regards