@media (max-width: 991.98px) {
    .navbar {
        position: relative;
        z-index: 9999;
    }

    #navbarNav {
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        width: 100%;
        background: #fff;
        z-index: 99999;
        max-height: calc(100vh - 80px);
        overflow-y: auto;
    }

    #navbarNav.show {
        display: block !important;
        visibility: visible !important;
        opacity: 1 !important;
    }
}