Have you tried using the mendix sidebar toggle button in your navigation layout?
Heres some documentation on layouts and the sidebar toggle button
https://docs.mendix.com/refguide/layout
https://docs.mendix.com/refguide/sidebar-toggle-button
I was attempting to use a side menu similar to following (with anchor links for a long FAQ page) -
http://getbootstrap.com/docs/3.3/examples/offcanvas/#
Added required js, and css to custom css. The toggle didn't seem to work and I later realized that default bootstrap navbar doesn't work either.