body
{	

	background-position: center center; 
	background-repeat: no-repeat;
	background-attachment: fixed;
	background-size: cover;
	background-color: #333300;
}


/* Ahora podemos cambiar solo la propiedad background-image */
@media (min-width: 480px) {
    body {
        background-image: url("../img/fondo-480.png");
    }
}
@media (min-width: 768px) {
    body {
        background-image: url("../img/fondo-760.png");
    }
}
@media (min-width: 1200px) {
    body {
        background-image: url("../img/fondo.png");
    }
}


#div_principal
{
	background-color: white;
	padding:20px;
	border-radius: 10px;
}

  .container{
  	max-width: 450px;  	
  }

  .container-fluid{
  	max-width: 450px;  	
  }