.banner {
    height: 495px;
    overflow: hidden;
    position: relative;
}
.banner img {
    width: 100%;
}
@media only screen and (max-width: 768px) {
    .banner {
        height: 250px;
    }
    .banner>.slide-img>img {
        height: 250px;
        width: auto;
        min-width: 100%;
    }
}