html, * { margin:0; padding: 0;}
section{
    width: 100%;
    height: 100vh;
}
.section1 {
    background-image:url('https://unsplash.it/2509/1673?image=628');
    background-repeat:no-repeat;
    background-size:cover;
    background-position:center;
     position: relative;
}
.section2 {
    background-image:url('https://unsplash.it/2509/1673?image=633');
     background-repeat:no-repeat;
    background-size:cover;
    background-position:center;
}
.section3 {
    background-image:url('https://unsplash.it/2509/1673?image=649');
    background-repeat:no-repeat;
    background-size:cover;
    background-position:center;
}