css3画太极图

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
    <title>太极图</title>
    <style type="text/css">
        .main {
            width: 150px;
            height: 300px;
            margin: 100px auto;
            border-radius: 150px;
            border:1px solid gray;
            border-left: 150px solid black;
        }
        .circle {
            width: 0px;
            height: px;
            padding: 25px;
            border-radius: 75px;
            margin-left: -75px;
        }
        .black {
            border:50px solid black;
            background: white;
        }
        .white {
            border:50px solid white;
            background: black;
        }
    </style>
</head>
<body>
    <div class="main">
        <div class="circle black"></div>
        <div class="circle white"></div>
    </div>
</body>
</html>