*{
        margin:0;
        padding:0;
    }
    nav{
        width: 1003px;
        height: 270px;
        margin:0px 0px 3px 0px;
        overflow: hidden;
        position: relative;
    }
    #index{
        position: absolute;
        left:850px;
        bottom: 25px;
    }
    #index li{
        width:8px;
        height: 8px;
        border: solid 1px gray;
        border-radius: 100%;
        background-color: #eee;
        display: inline-block;
    }
    #img{
        width: 1003px;
        height: 270px;
    }
    #img li{
        width: 1003px;
        height: 270px;
        position: absolute;/*必须设置为absolute，否则第一个li会把后面的都覆盖*/
        z-index: -1;
        opacity: 0;
        transition: opacity 1s ease-in;
    }
    #index .on{
        background-color: black;
    }
    #img .opa-on{
        opacity: 1;
    }