Adjust local.css to style sidebars for older ikiwiki versions.

Adjust local.css to style sidebars for older ikiwiki versions.

ikiwiki versions before
  commit baaa848f6c06b0b3a59677d3551e130c65e5fde7
  Author: Joey Hess <joey@gnu.kitenet.net>
  Date:   Thu Apr 15 15:04:17 2010 -0400
use id="sidebar" (newer version use class="sidebar"), so we repeat the
sidebar styling with
  .sidebar -> #sidebar
Now this style sheet will work with both versions.

Note that we also adjust #sidebar's padding, since that changed as
well.
  commit 5143d790b023f7f04ebdf694225b2946af676503
  Author: Joey Hess <joey@gnu.kitenet.net>
  Date:   Thu Apr 15 16:08:33 2010 -0400