<!DOCTYPE htm>

<meta charset="utf-8">

<meta name="viewport" content="width=device-width, initial-scale=1.0">

<link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">

<script src="https://cdn.bootcss.com/jquery/1.12.4/jquery.js"></script>

<script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

<style>body {margin:20px}</style>

<div class="alert alert-warning">

    <a href="#" class="close" data-dismiss="alert">

        ×

    </a>

    <strong>警告！</strong>您的网络连接有问题

</div>

​