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

body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-content: center;
    background: #000000;
}

nav {
   min-height: 10%;
}

main {
    min-height: 80%;
    justify-content: center;
    align-content: center;
}

footer {
    min-height: 10%;
}

main img,
footer img {
    display: block;
    margin-left: auto;
    margin-right: auto;
    max-width: 90%;
}