app {
    display: grid;
    width: 100%;
    height: 100%;
    grid: "nav" 56px
          "main" auto
          "footernav" 56px
          / 1fr;
}

#topnav {
    grid-area: nav;
}

.footernav {
    grid-area: footernav;
}

.footer {
    grid-area: footer;
}

main {
    grid-area: main;
}

@media (min-width: 1025px) {
    app {
        display: grid;
        width: 100%;
        height: 100%;
        grid: "nav" 88px
            "main" auto
            "footer" 79px
            / 1fr;
    }
    .footernav {
        display: none;
    }
}