怎么转不了呢，要用什么格式啊；
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
#bb{width: 100px; height: 100px; background: red; transform:rotate(0deg);}
</style>
</head>
<body>
<div id="bb">
</div>
<script type="text/javascript">
var a=40;
document.getElementById('bb').style.transform="rotate(a+'deg')";
</script>
</body>
</html>
