<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<style>
body {
margin: 0;
padding: 0;
background-color: #999;
}
.box {
background-color: #6cf;
width: 750px;
height: 10px;
margin: auto;
}
.line {
margin-top: 20px;
height: 10px;
background-color: #000;
width: 100%;
}
</style>
<div class="box"></div>
<div class="line"></div>
</body>
</html>
如果去掉理想视口，margin：auto; 会多出边距；
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
