<div class="container">
  <h3>全ての列に.oreder-クラスを設定した例</h3>
  <div class="row">
    <div class="col order-3">
      <em>1番目に記述</em><br>
     .order-3
    </div>
    <div class="col order-1">
      <em>2番目に記述</em><br>
      .order-1
    </div>
    <div class="col order-2">
     <em> 3番目に記述</em><br>
      .order-2
    </div>
  </div>
  
  <h3>.order-クラス指定なし、.order-クラス指定ありを混在させた例</h3>
  <div class="row">
    <div class="col">
      <em>1番目に記述</em><br>
     .order-指定なし
    </div>
    <div class="col order-2">
      <em>3番目に記述</em><br>
      .order-2
    </div>
    <div class="col">
      <em>3番目に記述</em><br>
     .order-指定なし
    </div>
    <div class="col order-1">
      <em>4番目に記述</em><br>
      .order-1
    </div>
  </div>
</div>
.row > [class*=col] {
    padding-top: .75rem;
    padding-bottom: .75rem;
    background-color: rgba(86,61,124,.15);
    border: 1px solid rgba(86,61,124,.2);
}

.row {
  margin-top: 1rem;
}
h3 {
  margin-top: 1rem;
  font-size: 1.5em;
  text-align: center;
  margin-top: 1em;
}

em {
  font-weight:bold;
  font-style:normal;
  font-size: 1.1em;
}

External CSS

  1. https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-beta.2/css/bootstrap.css

External JavaScript

This Pen doesn't use any external JavaScript resources.