<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}
html,
body {
width: 100%;
height: 100%;
}
.outer {
width: 400px;
height: 100%;
background: blue;
margin: 0 auto;
display: flex;
align-items: center;
}
.inner {
position: relative;
width: 100%;
height: 0;
padding-bottom: 50%;
background: red;
}
.box {
position: absolute;
width: 100%;
height: 100%;
display: flex;
justify-content: center;
align-items: center;
}
</style>
</head>
<body>
<div class="outer">
<div class="inner">
<div class="box">hello</div>
</div>
</div>
</body>
</html>
