div不定宽高的居中方式

方法1

.demo1{
    position:absolute;
    top:50%;
    left: 50%;
    -webkit-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
}

方法2

.demo2{
    display: flex;
    align-items: center;
    justify-content: center;
}

方法3

.parent-panel2:after{
    content:"";
    display: inline-block;
    vertical-align: middle;
    height: 100%;
}

定宽度

.demo4{
    position:absolute;
    top:50%;
    left:50%;
    margin-top:(width/2);
    margin-left:(width/2);
}