div盒子的居中设置

1. div盒子有宽度的

 .login-box {
    width: 555px;
    height: 423px;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    margin: auto;
  }

2. div 盒子没有固定宽度

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