.cu-background-wrapper {opacity: 0;transition:1s;}
.cu-background {background-image: url(../images/bg-cards.jpg);height: 100vh;z-index: -1;opacity: 1;background-position: center;transition: opacity 1s;}

.cu-content {display: none}

@media only screen and (max-width : 680px)
					{ 
		
						.cu-background {opacity: 0.5;}
				
					}