message: Open context selector over left sidebar
diff: left: 0;
  position: fixed;
  right: 0;
  - z-index: $zindex-navbar-fixed;
  + // The z-index of the masthead needs to be greater than the left sidebar so
  + // that the context selector opens over it.
  + z-index: $zindex-navbar-fixed + 1;
  @media (max-width: $grid-float-breakpoint-max) {
  padding-left: 50px; // make space for .sidebar-toggle
  }
  