devdocs/assets/stylesheets/pages/_react.scss

._react {
  > h2 { @extend %block-heading; }
  > h3 { @extend %block-label, %label-blue; }
  > h4 { @extend %block-label; }

  p code { @extend %label; }
  blockquote { @extend %note; }

  span.platform { float: right; }
  span.propType, span.platform { font-weight: normal; }
}