* {
	padding: 0;
	margin: 0;
	border: 0;
}
	
body { 
	height: 100%;
	width: 100%;
	display: table;
	_position: relative;
	/*overflow: hidden;*/
}
	
#mainContainer {
	_position: absolute;
	_top: 50%;
	display: table-cell;
	vertical-align: middle;
	text-align: center;
	width: 100%;
}
	
#mainDiv { 
	position: relative;
	_top: -50%;
	margin: 0 auto;	
}

/**
<body>

    <div class="A">
      <div class="mainDiv">
      </div>
    </div>

</body>
/