Left-sidebar navigation automatically takes over whole screen when the window is minimized

[crathbun428]

Steps to Reproduce

1. Login as an admin user to ensure the courseware.enable_navigation_sidebar waffle flag is enabled
2. Navigate to an in-course experience page
3. With the sidebar navigation expanded, minimize the browser window
4. Use your curser to make the window more narrow

Expected Behavior

1. The sidebar navigation remains expanded until a certain breakpoint (the point at which both the sidebar navigation and the course content can no longer fit side by side)
2. Once the window gets to the breakpoint described in Expected Behavior 1, the course content takes up the screen and the sidebar navigation expand button appears in the upper corner of the page
3. When the expand button is clicked, the sidebar navigation can take up the entire width of the window, but must be collapsable

Expected Behavior

1. The sidebar navigation remains expanded until a certain breakpoint (this current breakpoint feels sooner than the point at which both the sidebar navigation and the course content can no longer fit side by side)
2. Once the window gets to the breakpoint described in Actual Behavior 2, the sidebar navigation can take up the entire width of the window, but is collapsable