html

<div class="xcs-log"></div>

css

.xcs-log {
	text-align: center;
	/* padding: 0 15%; */
	background: url(../img/bg-1.jpg);
	background-position: 0px 0px;
	background-repeat: no-repeat;
	background-size:100% 100%;
}

JS

var iphoneHeight= $(window).height();
var iphoneWidth = $(window).width();
// console.log(iphoneHeight)
$(".xcs-log").css({
	"height":iphoneHeight,
	"width":iphoneWidth
})