<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>背景图撑开盒子高度</title>
<style>
.bg-box {
background-image: url(../demo.jpg);
background-size: 100% 100%;
background-repeat: no-repeat;
margin:0 auto;
}
.bg-box::after {
content: "";
display: block;
/*这里的padding = height / width*/
padding:20%;
}
</style>
</head>
<body>
<div class="bg-box"></div>
</body>
</html>