Due to how the line links now reside outside of the source lines, hovering over
line numbers doesn't count as hovering over the appropriate source line. It can
be worked around by using a "+" css selector. However, it's necessary to
reorder the elements and put <a> before <span> (which is actually quite
logical). It works without further css tweaks because <a> is already
absolute-positioned and so the order doesn't matter visually.
bbea50b708