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.hero{	
display:block;
width:100%;
height:400px;
background-image: url(https://upload.wikimedia.org/wikipedia/commons/d/d6/Half_Dome_from_Glacier_Point,_Yosemite_NP_-_Diliff.jpg);
background-repeat: no-repeat;
background-position: center center;
background-attachment: fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size:cover;

}