.banner {
    width: 350px;
    height: 250px;
    margin: 5px ;
    border: 1px solid #808080;
    position: relative;
    overflow: hidden;
}

.banner .img {
    width: 5000px;
    position: absolute;
    left: 0px;
    top: 0px;
}

.banner .img img {
    width: 500px;
    height: 300px;
}

.banner .img li {
    float: left;
}

.banner .num {
    position: absolute;
    width: 100%;
    bottom: 10px;
    left: 0px;
    text-align: center;
    font-size: 0px;
}

.banner .num li {
    width: 10px;
    height: 10px;
    background-color: #888;
    border-radius: 50%;
    display: inline-block;
    margin: 0px 3px;
    cursor: pointer;
}

.banner .num li.on {
    background-color: #ff6a00;
}

.banner .btn {
    width: 30px;
    height: 50px;
    background-color: #808080;
    opacity: 0.5;
    filter: alpha(opacity 0.5);
    position: absolute;
    top: 50%;
    margin-top: -25px;
    cursor: pointer;
    text-align: center;
    line-height: 50px;
    font-size: 40px;
    color: #fff;
    font-family: "宋体";
    display: none;
}

.banner .btn_l {
    left: 0px;
}

.banner .btn_r {
    right: 0px;
}

.banner:hover .btn {
    display: block;
}