message: Reduce .co-namespace-selector__menu.dropdown-menu max-height...
  to fix double scrollbar issue when a global notification is present.  Note:  at the smallest viewport heights, the double scrollbar issue can still exist when multiple notifications are present.  Given this is an unlikely scenario, it seems plausible to let it stand.
diff: -$co-namespace-selector-desktop: 47px;
  -$co-namespace-selector-mobile: 35px;
  $color-dropdown-hover: rgba(0, 0, 0, .05);
  $color-bookmarker--hover: #AAA;
  $color-bookmarker: #DDD;
  -$masthead-height: 76px;
  .dropdown {
  position: relative;
  @@ -185,14 +182,13 @@ $masthead-height: 76px;
  }
  .co-namespace-selector__menu.dropdown-menu {
  - max-height: calc(100vh - (#{$masthead-height} + #{$co-namespace-selector-mobile}));
  + max-height: 60vh;
  max-width: 100%;
  min-width: 210px;
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
  @media (min-width: $grid-float-breakpoint) {
  - max-height: calc(100vh - (#{$masthead-height} + #{$co-namespace-selector-desktop}));
  min-width: 250px;
  }
  