devdocs/assets/stylesheets/pages/_rust.scss

._rust {
  @extend %simple;

  h4 { @extend %block-label; }
  .docblock { margin-left: 1em; }

  div.stability { margin-bottom: 1em; }
  em.stab, span.stab { @extend %label; }
  em.stab.unstable, span.stab.unstable { @extend %label-orange; }
}