html, body{
    margin: 0;
    padding: 0;
}
.main {
    height: 100%;
    width: 100%;
    display: flex;
}
.nav {
    height: 100%;
    width: 20%;
}
@media (max-width: 600px) {
    .main {
        flex-direction: column;
    }
    .nav {
        height: 20%;
        width: 100%;
    }
}