使用animation-direction属性可以先向后运行动画，然后再向前运行动画。该属性与交替反向动画值一起使用可实现此目的。
<!DOCTYPE html>
<html>
<head>
<style>
div {
width: 150px;
height: 200px;
position: relative;
background-color: yellow;
animation-name: myanim;
animation-duration: 2s;
animation-direction: alternate-reverse;
animation-iteration-count: 3;
}
@keyframes myanim {
0% {background-color:green; left:0px; top:0px;}
50% {background-color:maroon; left:100px; top:100px;}
100% {background-color:gray; left:0px; top:0px;}
}
</style>
</head>
<body>
<div></div>
</body>
</html>