遇到的问题

<div id="bnts">
    <span class="on"></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
</div>

    #bnts span {
        cursor: pointer;
        float: left;
        border: 1px solid #FFF;
        width: 10px;
        height: 10px;
        border-radius: 50%;
        background: #333;
        margin-right: 5px;
    }
    #bnts .on {
        background: #FFF;
    }