As Ezio noted, the coming versions of the Python 3 documentation
provide a way to collapse the sidebar completely.  Perhaps a min-width
should be specified, but I'm not convinced that's a good idea.

The sidebar problem is fairly significant, and the collapsing sidebar
alone isn't sufficient.  The sidebar is useful since it's the only
overall navigation structure (as opposed to the direct links embedded
in the content), but there's no real need to ensure it gets "enough"
width.  I'd rather see a simple adjustment as recommended by
Christopher Dunn.

I appreciate Ezio's in making the sidebar collapsible, but I think
that's just the first step.  The sidebar is certainly the most
contentious element of the new design, and the most difficult to get
right.