Lebar tombol default di bootstrap arah fleksibel kolom

<body>
  <div class="container">
    <div class="row pt-4" id="cards">
      <div class="card-deck">
        <div class="card">
          <div class="card-body d-flex flex-column">
            <div>  <!-- Just wrap anchor/button in another div --> 
              <a href="#" class="btn btn-primary mt-auto">Set a Goal</a>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</body>
Repulsive Rhinoceros