CSS3绘制环形进度条

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        *{margin: 0;padding: 0;}
        .box{width:200px;height:200px;margin:10px auto;position:relative;}
        .box div{position:absolute;top:0;left:0;border-radius:50%;height:160px;width:160px;-webkit-transition:all .2s ease-in-out;-moz-transition:all .2s ease-in-out;}
        .box .bg{border:silver 20px solid}
        .box .bg2{border:silver 20px solid;clip:rect(0,100px,200px,0);}
        .box .rount{border:green 20px solid;clip:rect(0,100px,200px,0);-webkit-transform:rotate(0deg);}
        .box .rount2{border:green 20px solid;clip:rect(0,200px,200px,100px);-webkit-transform:rotate(0deg);display:none}
        .box .num{font:bold 24px/160px tahoma;text-align:center;color:green;top:20px;left:20px;z-index:9;}
        .points{width:200px;margin:10px auto;text-align: center;}
    </style>
    <script src="../jquery-1.7.2.js"></script>
    <script>
        $(function(){
            var points = $('#points'),
                    rount = $('#rount'),
                    rount2 = $('#rount2'),
                    num = $('#num');

            points.change(function(){
                var n =points.val();
                num.text(n + '%');
                if(n<=50){
                    rount.css('-webkit-transform','rotate(' + 3.6*n + 'deg)');
                    rount2.css('display','none');
                }else{
                    rount.css('-webkit-transform','rotate(180deg)');
                    rount2.css('display','block');
                    rount2.css('-webkit-transform','rotate(' + 3.6*(n-50) + 'deg)');
                }
            })
        })



    </script>
</head>
<body>
    <div class="box">
        <div class="bg"></div>
        <div id="rount" class="rount"></div>
        <div class="bg2"></div>
        <div id="rount2" class="rount2"></div>
        <div id="num" class="num">0</div>
    </div>
    <div class="points">
        <span>0</span>
        <input type="range" id="points" min="0" max="100" step="1" value="0">
        <span>100</span>
    </div>
</body>
</html>
测试结果：