<title>Font Awesome 图标</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdn.staticfile.org/font-awesome/4.7.0/css/font-awesome.css">
<h1>fa fa-envelope-open-o</h1>
<i class="fa fa-envelope-open-o"></i>
<i class="fa fa-envelope-open-o" style="font-size:24px"></i>
<i class="fa fa-envelope-open-o" style="font-size:36px"></i>
<i class="fa fa-envelope-open-o" style="font-size:48px;color:red"></i>
<button style="font-size:24px">按钮 <i class="fa fa-envelope-open-o"></i></button>
<i style="font-size:24px" class="fa">数据缺失！</i>
