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代码编辑器：

<!DOCTYPE html>
<meta charset="utf-8">
<link href="/static/next/css/tryit.css?v=2017082407" rel="stylesheet"/> 
<style> 
div
{
	width:100px;
	height:100px;
	background:red;
	position:relative;
	animation:myfirst 5s infinite;
	animation-direction:alternate;

/* Safari 和 Chrome */
	-webkit-animation:myfirst 5s infinite;
	-webkit-animation-direction:alternate;
}

@keyframes myfirst
{
	0%   {background:red; left:0px; top:0px;}
	25%  {background:yellow; left:200px; top:0px;}
	50%  {background:blue; left:200px; top:200px;}
	75%  {background:green; left:0px; top:200px;}
	100% {background:red; left:0px; top:0px;}
}

@-webkit-keyframes myfirst /* Safari 和 Chrome */
{
	0%   {background:red; left:0px; top:0px;}
	25%  {background:yellow; left:200px; top:0px;}
	50%  {background:blue; left:200px; top:200px;}
	75%  {background:green; left:0px; top:200px;}
	100% {background:red; left:0px; top:0px;}
}
</style>

<p><strong>注意：</strong>Internet Explorer 9 及其之前的版本不支持 animation-direction 属性。</p>

代码编辑器：

运行结果：