.tab * {
    margin: 0;
    padding: 0;
    list-style-type: none;
}

.tab {
    width: 638px;
    height: 283px;
    overflow: hidden;
    margin: 5% auto 0 auto;
}

.tab a, .tab img {
    border: 0;
}

.tab .tab_pic ul {
    height: 283px;
    width: 999em;
    position: relative;
}

.tab .tab_pic ul li {
    float: left;
}

.tab .tab_pic ul li a {
    display: block;
}

.tab_pic {
    float: left;
    width: 225px;
    height: 283px;
    overflow: hidden;
    position: relative;
}

.tab_txt {
    float: right;
    width: 413px;
    height: 283px;
    overflow: hidden;
    position: relative;
}

.tab .tab_pic .prev, .tab .tab_pic .next {
    display: block;
    width: 31px;
    height: 31px;
    float: right;
    margin: 0 0 0 1px;
    overflow: hidden;
    cursor: pointer;
}

.tab .tab_txt ul {
    position: relative;
}

.tab .tab_txt ul li {
    width: 413px;
    height: 270px;
    padding: 10px 20px;
    float: left;
}

.tab_san {
    display: block;
    width: 17px;
    height: 34px;
    position: absolute;
    top: 29px;
    right: 0;
}

.btn_bg {
    width: 225px;
    height: 33px;
    display: block;
    position: absolute;
    left: 0;
    bottom: 0;
    z-index: 1;
    background: #000;
    display: block;
    filter: alpha(opacity=30);
    -moz-opacity: 0.3;
    -khtml-opacity: 0.3;
    opacity: 0.3;
}

.btn_ct {
    width: 225px;
    height: 31px;
    padding: 1px;
    display: block;
    position: absolute;
    left: 0;
    bottom: 0;
    z-index: 2;
}
@media (max-width: 768px) {
    .tab{margin-top: 0;overflow-y: scroll}
    .tab_pic{
        float: none;
    }
    .tab_txt{
        float: none;
    }

    .tab .tab_txt ul {
        height: 250px;
    }
}