div水平和垂直居中显示

.div1{

    width: 100px;
    height: 100px;
    border: 4px solid red;
    position: absolute;

    text-align: center;

    left:0;
    right:0;
    top: 0;
    bottom: 0;
    margin: auto;
    /*50%为自身尺寸的一半*/
}

效果如图