.xl_banner {
    height: 460px;
    background-size: 100%;
    background-repeat: no-repeat;
    background-position: center;
}

@media screen and (max-width: 1200px) {
    .xl_banner {
        background-size: 290%;
        height: 180px;
    }
}
.jianjieimg{
    width: 100%;
    height: auto;
    margin: auto;
}