data-dismiss是bootstrap里自定义的属性，给一个元素data-dimiss属性的话，可以通过点击该元素达到让目标消失的效果。
例如：当点击按钮时，直接关闭外层alert
<div class="alert alert-warning alert-dismissible" role="alert1">
<button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
<strong>Warning!</strong> Better check yourself, you're not looking too good.
</div>
