Mixin regression

[winstliu]

.markdown-preview[data-use-github-style] {
  .markdown-body(); // comment this out to fix everything

  padding: 30px; // padding is property-value
  font-size: 16px; // entity.name.tag.custom
  color: #333; // support.type.property-name.media
  background-color: #fff; // entity.name.tag.custom
  overflow: scroll; // no scope

  a {
    color: #337ab7;
  }
}