Bootstrap class: .card-body

<div class="card">
  <div class="card-body">
    This is some text within a card block.
  </div>
</div>

Preview

This is some text within a card block.

Sass source

/* _card.scss:34 */
.card-body {
  // Enable `flex-grow: 1` for decks and groups so that card blocks take up
  // as much space as possible, ensuring footers are aligned to the bottom.
  flex: 1 1 auto;
  padding: $card-spacer-x;
}

Uses variables

/* _card.scss:34 */
$card-spacer-x