There are a few rough edges on how the side panels are navigated.
[ ] There should always be an (X) icon to close the side panel at the top-right (in LTR) of the panel
[ ] Closing a side panel when losing work is a possibility should trigger an "Are you sure about that?" modal
[ ] Clicking the backdrop (the semi-transparent background behind the side panel) then it should be equivalent to clicking the (X) icon to close the side panel
[ ] When the user can navigate back within the side panel (ie, the user is navigating the tree of contents), then a back arrow should be present at the top-left (in LTR) of the panel. Clicking this should be equivalent to clicking the browser's back button.
Overview
There are a few rough edges on how the side panels are navigated.