html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
}

header {
    width: 100%;
    height: 4rem;
    display: flex;
    justify-content: center;
}

nav {
    width: 60%;
    height: 100%;
    max-width: 600px;
    display: flex;
    justify-content: space-around;
    align-items: center;
}

main {
    width: 100%;
    height: calc(100% - 4rem);
    display: flex;
    justify-content: center;
    align-items: center;
}

span {
    font-size: 24px;
}