漂亮的雪花图案：
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8">
<title>CSSAAA TEST DEMO</title>
<style type="text/css">
#snow {
margin:160px;position:relative;
width:200px;height:20px;
border-radius:25px;
background-color:#09f;
}
.flake {
position:absolute;left:0;right:0;top:0;bottom:0;margin:auto;
width:35px;height:10px;border-radius:10px;
}
#snow:before, #snow:after, .flake:before, .flake:after {
content:" ";position:absolute;
width:inherit;height:inherit;
border-radius:inherit;
background-color:inherit;
}
#snow:before, .flake:before {
transform:rotate(-60deg);
}
#snow:after, .flake:after {
transform:rotate(60deg);
}
.flake, .flake:before, .flake:after {
box-shadow:45px 50px 0 2px #09f,-45px -50px 0 2px #09f,
45px -50px 0 2px #09f,-45px 50px 0 2px #09f;
}
</style>
<script src="https://cdn.bootcss.com/prefixfree/1.0.7/prefixfree.min.js"></script>
</head>
<body>
<div id="snow">
<div class="flake"></div>
</div>
</body>
</html>
代码来自：http://www.cssaaa.com/css3/158.html
