User blog comment:DaNASCAT/Technical Update: June 12, 2017/@comment-3218221-20170613135028/@comment-25503930-20170613140046

Hey Rivriley, as part of the redesign we also announced that we will no longer be allowing most forms of CSS and JS customization to the headers. This includes adding fourth and fifth level sub-menus to Wiki Navigation. You can find more about that topic written here in this forum post.