方法1:web
position:absolute; top:50%; left: 50%; -webkit-transform: translate(-50%, -50%); transform: translate(-50%, -50%);
方法2:flex
display: flex; align-items: center; justify-content: center;
方法3:spa
.parent-panel2:after{ content:""; display: inline-block; vertical-align: middle; height: 100%; }
定寬度code
position:absolute; top:50%; left:50%; margin-top:(width/2); margin-left:(width/2);