.menu-item.menu-item-type-custom:last-child {
    margin-left: auto;
}

@media (min-width: 990px) {
    body #menu-main-menu {
        justify-content: center !important;
        padding-right: 260px;
        height: 54px;
    }

    body #menu-main-menu li.menu-item.menu-item-type-custom:last-child {
        position: absolute;
    }
}