This prevents list items from flowing into the same line when the text
is too short. That behavior is a consequence from switching display in
these items to inline-block, to enforce a bottom margin.

The other technique (left margin in pixels) was simpler and worked
well on Firefox 10.0 and Chromium 6 in Linux, but it was far from
perfect in Firefox 15 on Windows. This technique (position relative
in #box and "right 100%" in the tabs) is also more general, although
that should not be important in this project (we should not need any
other boxes with tabs).

The other technique (left margin in pixels) was simpler and worked
well on Firefox 10.0 and Chromium 6 in Linux, but it was far from
perfect in Firefox 15 on Windows. This technique (position relative
in #box and "right 100%" in the tabs) is also more general, although
that should not be important in this project (we should not need any
other boxes with tabs).