div.cn {
position: relative;
width: 200px;
height: 200px;
background: gray;
text-align: center;
}
div.inner {
position: absolute;
top: 50%;
left: 50%;
width: 100px;
height: 100px;
-webkit-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);
background: red;
}