<select multiple class="form-control">
  <option>1</option>
  <option>2</option>
  <option>3</option>
  <option>4</option>
  <option>5</option>
  <option>6</option>
  <option>7</option>
  <option>8</option>
  <option>9</option>
  <option>10</option>
  <option>11</option>
</select>

External CSS

  1. //maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css

External JavaScript

This Pen doesn't use any external JavaScript resources.