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Bootstrap class: .blockquote-footer

<blockquote class="blockquote">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
  <footer class="blockquote-footer">Someone famous in
    <cite title="Source Title">Source Title</cite>
  </footer>
</blockquote>

Preview

Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Someone famous in Source Title

Sass source

/* _type.scss:117 */
.blockquote-footer {
  display: block;
  font-size: 80%; // back to default font-size
  color: $blockquote-small-color;

  &::before {
    content: "\2014 \00A0"; // em dash, nbsp
  }
}

Uses variables

/* _type.scss:117 */
$blockquote-small-color