body {
  margin:0;
  margin-top:calc(100vh + 18px);
}


#un, #deux, #trois {
  width:100%;
  height:100vh;
/*   margin-bottom:4px; */
  background-size:cover;
}

#deux {
  height:130vh;
  background:#000;
}


#trois {
  background: url("../images/fondo-2.jpg") no-repeat top center #000;
  background-size:cover;
}


@media only screen and (min-width:0px) and (max-width:767px){
	
#trois {
  width:100%;
  height:auto;
}	
	
#deux {
  height:110vh;
}
	
}