使用nav-stacked时，如何在nav-pills中应用边框？

Question

在nav-pills中使用nav-stacked时，如何在左侧(或右侧，视情况而定)应用边界？

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<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>

<div class="row">
  <div class="col-md-9">
    <div class="tab-content">
      <div id="states" class="tab-pane fade in active">
        <h3>States</h3>
        <p>States tab</p>
      </div>
      <div id="subs" class="tab-pane fade">
        <h3>Subscriptions</h3>
        <p>Subscriptions tab</p>
      </div>
      <div id="comments" class="tab-pane fade">
        <h3>Comments</h3>
        <p>Comments tab</p>
      </div>
    </div>
  </div>

  <div class="col-md-3">
    <ul class="nav nav-pills nav-stacked" id="myTabs">
      <li class="active">
        <a href="#states" data-toggle="tab">
          States
        </a>
      </li>
      <li>
        <a href="#subs" data-toggle="tab">
          Subscriptions
        </a>
      </li>
      <li>
        <a href="#comments" data-toggle="tab">
          Comments
        </a>
      </li>
    </ul>
  </div>
</div>

​