<div class="d-flex flex-column justify-content-center container">
<blockquote class="blockquote">
  <p class="mb-0">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
  <footer class="blockquote-footer">Someone famous in <cite title="Source Title">Source Title</cite></footer>
</blockquote>
<div>

html, body {
  display: grid;
  height: 100%;
}