I’m still working on my mobile navigation, and I ran across a weird problem. When you visit a parent page, the children links then show - just as I wanted. But when you visit a child page, the children navigation elements lose their color.
However when the child is the current item the cuurrent_page_item class is replaced by current_page_parent class so I would assume you need to target that in the same way.
e.g.
#main-nav_responsive .page-item-11.current_page_item a,
#main-nav_responsive .page-item-11.current_page_parent a {
background: none repeat scroll 0 0 #2CA7E1;
}