how to set center field in bootsatrap code example

Example 1: set textbox into center of div in bootstrap

<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-alpha/css/bootstrap.css" rel="stylesheet" />
<td style="background:#B3AEB5;">
  <div class="form-group text-center">
    <div class="input-group" style="margin:auto;">
      <input type="month" name="p2" value="test">
    </div>
  </div>
</td>

Example 2: center form group bootstrap

.class {
    margin: 0 auto;
    float: none; //optional
}