Bootstrap col-xs-push-12 col-xs-pull-12

Question

我现在想犯错误的地方？它没有发生：

5      7

到

7
5

<div class="col-md-5 col-xs-12 col-xs-pull-12">5</div>
<div class="col-md-7 col-xs-12 col-xs-push-12">7</div>