<html>
<style>
.parent {
display: table-cell;
text-align: center; /*水平居中*/
vertical-align: middle; /*垂直居中*/
width:300px;height:300px;
background: red;
}
.child {
display:inline-block;
width: 50px;
height: 50px;
background: green;
line-height: 50px;
text-align: center;
color: white;
}</style>
<body>
<div class="parent">
<div class="child">Demo</div>
</div>
</body>
</html>
