css/modules/primer-markdown/lib/lists.scss

// Base styles
// stylelint-disable selector-no-qualifying-type
// stylelint-disable selector-max-type
.markdown-body {

  // Lists, Blockquotes & Such
  ul,
  ol {
    padding-left: 2em;

    &.no-list {
      padding: 0;
      list-style-type: none;
    }
  }

  // Did someone complain about list spacing? Encourage them
  // to create the spacing with their markdown formatting.
  // List behavior should be controled by the markup, not the css.
  //
  // For lists with padding between items, use blank
  // lines between items. This will generate paragraphs with
  // padding to space things out.
  //
  // - item
  //
  // - item
  //
  // - item
  //
  // For list without padding, don't use blank lines.
  //
  // - item
  // - item
  // - item
  //
  // Modifying the css to emulate these behaviors merely brakes
  // one case in the process of solving another. Don't change
  // this unless it's really really a bug.
  ul ul,
  ul ol,
  ol ol,
  ol ul {
    margin-top: 0;
    margin-bottom: 0;
  }

  li > p {
    margin-top: $spacer-3;
  }

  li + li {
    margin-top: 0.25em;
  }

  dl {
    padding: 0;

    dt {
      padding: 0;
      margin-top: $spacer-3;
      font-size: 1em;
      font-style: italic;
      font-weight: $font-weight-bold;
    }

    dd {
      padding: 0 $spacer-3;
      margin-bottom: $spacer-3;
    }
  }
}