<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>变大</title>
</head>
<style>
.box{
width: 200px;
height: 200px;
margin: 200px auto;
background: royalblue;
animation: fangkuai 4s alternate infinite;
}
@keyframes fangkuai{
from{transform: scale(0);}
to{transform: scale(1);}
}
</style>
<body>
<div class="box"></div>
</body>
</html>