<head lang="en">
<meta charset="UTF-8">
<title></title>
<style type="text/css">
.box{
display:block;
height:350px;
width:250px;
background:#ddd;
cursor:pointer;
-webkit-transition: 0.4s;
-moz-transition: 0.4s;
-ms-transition: 0.4s;
-o-transition: 0.4s;
transition: 0.4s;
}
.box:hover{
border-top-right-radius:180px 120px;background: rgba(246,246,247,0.9);
}
</style>
</head>
<body>
<a class="box"></a>
</body>
</html>
border-radius结合transition的一个小应用（动画）
原文：http://www.cnblogs.com/wangying731/p/5532007.html