devdocs/assets/stylesheets/pages/_phpunit.scss

._phpunit {
  > h2 { @extend %block-heading; }
  > h3 { @extend %block-label, %label-blue; }
  > h4 { font-size: 1em; }

  > p > code { @extend %label; }

  .warning, .alert {
    @extend %note;

    > h3 {
      margin: 0 0 .5em;
      font-size: 1em;
    }
  }

  .alert-danger { @extend %note-red; }
}