@media(max-width: 999px) {
    .single-product .summary form.cart .ct-cart-actions {
        position: fixed;
        bottom: 0;
        left: 0;
        width: 100%;
        z-index: 99999;
        padding: 10px 10px 0 10px;
        background: #f8f9fb;
    }

    .single-product .summary form.cart {
        margin-bottom: 0px !important;
        padding-bottom: 0px !important;
        border-bottom: unset;
    }
}