body {
    margin: 0;
    padding: 0;
    font-family: sans-serif;
    font-size: 19px;
}
section {
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    width: 100%;
    height: 100vh;
}
#s1 {
    background-image: url(images/01.jpg);  
}
#s2 {
    background-image: url(images/02.jpg);
}
#s3 {
    background-image: url(images/03.jpg);
}
article {
    padding: 50px;
    background-color: #f3f3f3;
    text-align: center;
}