主要是使用 css3的animation，scale等于1是原图大小，大于1是把图片放大，小于1 是把图片缩小。animation-delay用来延迟5秒触发这个动画
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}
body {
100%;
height: 100%;
overflow: hidden;
}
.outBox,
.innerBox {
100%;
height: 100%;
}
.outBox {
overflow: hidden;
}
.innerBox {
100%;
height: 100%;
animation: changeBiger 4s linear forwards;
animation-delay: 5s;
-webkit-animation-delay: 5s;
transform: scale(1.08);
}
@keyframes changeBiger {
0% {
transform: scale(1.08);
}
100% {
transform: scale(1);
}
}
.innerBox {
background-size: cover;
background-repeat: no-repeat;
background-position: center center;
background-image: url(https://ss1.baidu.com/9vo3dSag_xI4khGko9WTAnF6hhy/image/h%3D220/sign=627199341fce36d3bd0484320af13a24/ae51f3deb48f8c54ad2aa0c130292df5e1fe7f66.jpg);
}
</style>
</head>
<body>
<div class="outBox">
<div class="innerBox">
<!--<img src="https://ss1.baidu.com/9vo3dSag_xI4khGko9WTAnF6hhy/image/h%3D220/sign=627199341fce36d3bd0484320af13a24/ae51f3deb48f8c54ad2aa0c130292df5e1fe7f66.jpg" alt="">-->
</div>
</div>
</body>
</html>