message: Update sidebar CSS selector.
  This corrects a bug where the CSS selcetor to reposition the top of the
  rustdoc sidebar was no longer applied to the element. It also updates
  the magic number to be less magic.
  Fixes
diff: @@ -51,7 +51,7 @@ div.rustdoc {
  top: $top-navbar-height;
  .sidebar-elems.show-it {
  - top: 77px;
  + top: 45px + $top-navbar-height;
  }
  #sidebar-filler {
  