body {
    margin: 0;
    padding: 0;
    height: 100%;
    display: flex;
    justify-content: center;
    background-repeat: no-repeat;
    flex-direction: column;
    background-image: url('../pictures/background.png');
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    background-attachment: fixed;
}

.main-window, .main-window-secondary {
    width: 100%;
    text-align: center;
    background: rgb(207, 229, 247);
    margin: 0 0 8% 0;
    padding-top: 70px;
}

@media screen and (max-width: 768px) {
    body {
        background-image: url('../pictures/instruction.png');
    }
    .main-window, .main-window-secondary {
        padding-top: 55px;
    }
}

@media screen and (max-width: 480px) {
    .main-window, .main-window-secondary {
        padding-top: 40px;
    }
    .main-window-secondary {
        margin-bottom: 24vh;
    }
}