CSS를 이용해서 화면 가운데에 DIV 위치시키기
<head>
#imageViewer {
position: absolute;
z-index: 20;
left: 50%; top: 50%;
transform: translateX(-50%) translateY(-50%);
background-image: url('../img/grtc/detail/empty-630.png');
width: 630px; height: 424px;
}
</head>
<body>
<div id="imageViewer" style="display: none;">
<img src="<c:url value='/'/>img/grtc/detail/empty-630.png" onerror="<c:url value='/'/>img/grtc/detail/empty-630.png" alt="">
</div>
</body>