#form {
    max-width: 700px;
    margin: 16px;
}

#form h1 {
    margin: 30px 30px 40px;
    text-align: center;
}

#praat {
    display: block;
    margin-top: 16px;
    margin-bottom: 16px;
    width: 100%;
}

#veranderkleurtjes {
    position: fixed;
    bottom: 0;
    margin-bottom: 16px;

    /* And if you want the div to be full-width: */
    left: 0;
    right: 0;
}