body {
    margin: 0;
    min-height: 100vh;

    /* Bliss background */
    background: url("bliss.jpg") no-repeat center center fixed;
    background-size: cover;

    display: flex;
    flex-direction: column;   /* THIS is the important fix */
    align-items: center;
}

.window {
    margin-top: 60px;
}

footer {
    margin-top: auto; /* pushes footer to bottom */
    padding: 10px;
}