WordPress has a built in feature that assigns the class “current-menu-item” to the current navigation item.
Nevertheless, that feature only works for contextual menus; and not for the ones inside the post content.
You can see in this page that the first level parent item OBRAS is highlighted, but not the third level child GRÁFIKA located left in the inner page menu.
Looking for a method to accomplish this highlight feature in the inner menu.
Read more here:: Highlight inner post menu current item