app.component.scss

@media only screen and (min-width: 551px) {
    /* desktop */
    .mobile-menu{
        display:none;
    }

    .mobile{
        display:none;
    }
}

@media only screen and (max-width: 550px) {
    /* phones */
    .desktop{
        display:none;
    }
}

.mobile-menu{
    &.closed{
        display:none;
    }
}