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

div {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
}

.parallax1 {
      background: fixed no-repeat 50% 50%;
      background-color: black;
      background-size: cover;
      background-image: url(../images/buzon.jpg);
      
}

.parallax2 {
    background: fixed no-repeat 50% 50%;
    background-color: black;
    background-size: cover;
    background-image: url(../images/timbres.jpg);
}

.parallax3 {
    background: fixed no-repeat 50% 50%;
    background-color: black;
    background-size: cover;
    background-image: url(../images/casillas.jpg);
}