为什么圆点不加float:left就显示不出来，加了float:left就可以正常显示？
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
.btn {position: absolute;height: 10px;width: 100px;top: 20px;left: 250px;}
.btn span{float:right;cursor:pointer;border: 1px solid #fff;width: 10px;height: 10px;border-radius: 10px;background: #333;margin-right: 5px;}
</style>
</head>
<body>
<div class="btn">
<span>
</span>
</div>
</body>
</html>
