方法1:反向移动
position:absolute;
top:50%;
left: 50%;
-webkit-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);
方法2:flex布局
display: flex;
align-items: center;
justify-content: center;
方法3:四向定位
position: absolute;
right: 0;
left: 0;
top: 0;
bottom: 0;
margin: auto;
方法4:表格
father:
display:table;
text-algin:center;
son:
display:table-cell;
vertical-align:middle;