style>
        /*补充代码*/
        *{
            margin:0;
        }
        .box{
            position:relative;
        }
        .box .bd1{
            width:0px;
            height:0px;
            border:100px solid transparent;
            border-left-color:red;
            border-radius:80px;
        }
        .box .bd2{
            width:0px;
            height:0px;
            border:100px solid transparent;
            border-right-color:red;
            position:absolute;
            top:0;
            left:-10px;
            border-radius:80px;
        }

    </style>

​<div class="box">
        <div class="bd1"></div>
        <div class="bd2"></div>
</div>