1、什么是响应式 Web 设计？
- RWD 指的是响应式 Web 设计（Responsive Web Design）
- RWD 能够以可变尺寸传递网页
- RWD 对于平板和移动设备是必需的
2、使用 Bootstrap
Bootstrap 是最流行的开发响应式 web 的 HTML, CSS, 和 JS 框架。
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<div class="jumbotron">
<h1>W3School Demo</h1>
<p>Resize this responsive page!</p>
</div>
</div>
<div class="container">
<div class="row">
<div class="col-md-4">
<h2>London</h2>
<p>London is the capital city of England.</p>
<p>It is the most populous city in the United Kingdom,
with a metropolitan area of over 13 million inhabitants.</p>
</div>
<div class="col-md-4">
<h2>Paris</h2>
<p>Paris is the capital and most populous city of France.</p>
</div>
<div class="col-md-4">
<h2>Tokyo</h2>
<p>Tokyo is the capital of Japan, the center of the Greater Tokyo Area,
and the most populous metropolitan area in the world.</p>
</div>
</div>
</div>
</div>
</body>
</html>
