*水平居中* * 行内元素:`text-align: center` * 块级元素:`margin: 0 auto` * position:absolute +left:50%+ transform:translateX(-50%) * `display:flex + justify-content: center` *垂直居中* * 设置line-height 等于height * position：absolute +top:50%+ transform:translateY(-50%) * `display:flex + align-items: center` * display:table+display:table-cell + vertical-align: middle;