.nav {
    width: 100%;
    height: 70px;
    box-shadow: 0 3px 3px 0 #CCC;
    background: #393d49;
    position: fixed;
    left: 0;
    top: 0;
    z-index: 999;
    overflow: hidden;
    transition: 0.3s;
}
.banner-img {
    width: 100%;
}