nav {
    text-align: center;
    position: sticky;
    top: 10px;
    background-color: gray;
}

img {
    position: static;
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 100%;
}

main {
    position: relative;
}

.centered {
    position: absolute;
    top: 50%;
    width: 100%;
    text-align: center;
    background-color: aqua;
    color: red;
}

#copyright {
    position: relative;
    left: 10px;
}

#backToTop {
    position: fixed;
    bottom: 0;
    right: 0;
    background-color: aliceblue;
}