有的标签必须写，代码里有注释
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div{
width: 100px;
height: 100px;
/*必须设置相对于定位：relative*/
position: relative;
background-color: deeppink;
/*需要重复执行要添加csss属性infinite，默认会执行1次*/
animation: move 2s infinite;
}
@keyframes move {
from {top:0px;}
to{top:300px;}
}
</style>
</head>
<body>
<p>div自动向下移动</p>
<div></div>
</body>
</html>
