Submenu modyfication

hello,

I want to modify submenu in theme Editorial http://demo.mysterythemes.com/editorial/category/fashion/

Exacly convert submenu from vertical to horizontal layout

Im not looking modyfication in CSS, because it will work only when category in menu is a:hover.

Im looking for solution, when user is reading a post in subcategory and still see subcategories in menu

Visualisation

Thanks for solution / help / advice