._d3 {  > h2 { @extend %block-heading; }  > h3 { @extend %block-label; }  > h4 { font-size: 1rem; }  > h6 { @extend %block-label, %label-blue; }   > h6 > .source {    float: right;    font-weight: normal;  }   code { @extend %label; }  blockquote { @extend %note, %note-blue; }}