.back-top{
	background-position: 50% 0%;
	-webkit-background-size: cover;
  	-moz-background-size: cover;
  	-o-background-size: cover;
	background-size: cover;
}

.back-center{
	background-position: 50% 50%;
	-webkit-background-size: cover;
  	-moz-background-size: cover;
  	-o-background-size: cover;
	background-size: cover;
}

.back-bottom{
	background-position: 50% 100%;
	-webkit-background-size: cover;
  	-moz-background-size: cover;
  	-o-background-size: cover;
	background-size: cover;
}

#solar{
	background-image: linear-gradient(rgba(0,0,0,0.2),rgba(0,0,0,0.2)),
		url(../img/solar_3.jpg);
	color: white;
}

#instalacions{
	background-image: linear-gradient(rgba(0,0,0,0.2),rgba(0,0,0,0.2)),
		url(../img/instalacions_2.jpg);
	color: white;
}

#vertical{
	background-image: linear-gradient(rgba(0,0,0,0.2),rgba(0,0,0,0.2)),
		url(../img/verticals_2.jpg);
	color: white;
}

#enginyeria{
	background-image: linear-gradient(rgba(0,0,0,0.2),rgba(0,0,0,0.2)),
		url(../img/enginyeria_3.jpg);
	color: white;
}


/* Smartphones (portrait and landscape) ----------- */  
@media only screen and (min-width : 320px) and (max-width : 480px) {
	#solar{
		background-image: 
			linear-gradient(rgba(0,0,0,0.3),rgba(0,0,0,0.3)),
			url(../img/solar_3.jpg);
	}
	#solar img{
        	max-width: 300px;
    	}
	#instalacions{
		background-image: 
			linear-gradient(rgba(0,0,0,0.3),rgba(0,0,0,0.3)),
			url(../img/instalacions_2.jpg);
	}
	#instalacions img{
        	max-width: 300px;
    	}
	#vertical{
		background-image: 
			linear-gradient(rgba(0,0,0,0.3),rgba(0,0,0,0.3)),
			url(../img/verticals_2.jpg);
	}
	#vertical img{
        	max-width: 300px;
    	}
	#enginyeria{
		background-image: 
			linear-gradient(rgba(0,0,0,0.3),rgba(0,0,0,0.3)),
			url(../img/enginyeria_3.jpg);
	}
	#enginyeria img{
        	max-width: 300px;
    	}
}
	
/* iPads (portrait and landscape) ----------- */  
@media only screen and (min-width : 768px) and (max-width : 1024px) {  
	#solar img{
        max-width: 400px;
    }
    #instalacions img{
        max-width: 400px;
    }
    #vertical img{
        max-width: 400px;
    }
    #enginyeria img{
        max-width: 400px;
    }
}  
	
/* Desktops and laptops ----------- */  
@media only screen  and (min-width : 1224px) {  
	#solar img{
        max-width: 400px;
    }
    #instalacions img{
        max-width: 400px;
    }
    #vertical img{
        max-width: 400px;
    }
    #enginyeria img{
        max-width: 400px;
    }
}