@media only screen and (min-width:768px) { 
header{
	width: 100%;
	height: 450px;
	background: #9cecfb;;
	background: -webkit-linear-gradient(to right, hsla(0, 10%, 10%, 0.671), hsla(0, 10%, 10%, 0.671)), url("../img/fondo.jpg"); 
	background: linear-gradient(to right, hsla(0, 10%, 10%, 0.671), hsla(0, 10%, 10%, 0.671)), url("../img/fondo.jpg");
	background-size: cover;
	background-attachment: fixed;
	position: relative;
}

}