target menu item visibility

Hi

I wonder if someone can help; I;ve trying to target the menu or list of the selected menu item;

For example I have a man navigation and sub pages; when the sub page is selected the menu disappears – so is there a way for when a menu item in that sub nav is elected the visibility or opacity is changed;

So I almost want to target the current-menu-item’s list or menu;

Hope that makes sense