devdocs/assets/stylesheets/pages/_node.scss

._node {
  .api_stability_0, .api_stability_1 { @extend %note, %note-red; }
  .api_stability_2 { @extend %note; }
  .api_stability_3, .api_stability_4 { @extend %note, %note-green; }
  .api_stability_5 { @extend %note, %note-blue; }

  > h2 { @extend %block-heading; }
  > h3 { @extend %block-label, %label-blue; }
  > h4 { @extend %block-label; }
  > h2 + h2, > h3 + h3 { margin-top: 0; }

  > p > code, .type {
    white-space: normal;
    @extend %label;
  }
}