div不定寬高的居中方式

方法1:

 position:absolute;
    top:50%;
    left: 50%;
    -webkit-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);

方法2:

display: flex;
align-items: center;
justify-content: center;

方法3:

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

定寬度

position:absolute;
top:50%;
left:50%;
margin-top:(width/2);
margin-left:(width/2);