I think there must have been an update to OneNote recently because I used to be able to mouse over the side of the page and bring up the page/section bar and hide it just as easily. first it would open the page, and if you hit the back button it would open the full bar. This was much more convenient and made it easy to quickly navigate between pages/sections/notebooks. The functionality is much more limited with the new navigation system. Bring back the old system.