message: Fix z-index issues caused by `sticky-discussion-sidebar`
diff: +:root .pagehead ul.pagehead-actions {
  + z-index: initial; /* This affects the social buttons. It seems to have no effect but it constantly causes trouble with other features. */
  +}
  +
  .rgh-sticky-sidebar {
  position: sticky;
  top: 60px !important; /* Matches sticky header's height */
  - z-index: 31 !important;
  }
  /* Hides the last divider (on pull requests) to avoid https://user-images.githubusercontent.com/10238474/62282128-af6fb980-b457-11e9-8b18-c29687b88da1.gif */
  