.google-map {
    position: relative;
    width: 100%;    /* 左右に余白が必要なら値を変更してもOK */
    height: 0;
    padding-bottom: 45vw;    /* padding-topでもOK */
    overflow: hidden;
}
.google-map iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;    /* 必要であれば!importantを付けてください */
    height: 100%;    /* 必要であれば!importantを付けてください */
}
@media screen and (max-width: 991px){
    .navbar-collapse:before {
        background: #f96332;
        background: -webkit-linear-gradient(#f96332 0%, #000 80%);
        background: -o-linear-gradient(#f96332 0%, #000 80%);
        background: -moz-linear-gradient(#f96332 0%, #000 80%);
        background: linear-gradient(#f96332 0%, #000 80%);
        opacity: 0.76;
        filter: alpha(opacity=76);
        display: block;
        content: "";
        position: absolute;
        width: 100%;
        height: 100%;
        top: 0;
        left: 0;
        z-index: -1;
    }
}