盒子上下左右居中

.person-empty{position: fixed;
 position: fixed;
 left: 30%;
 right: 0;
 top: 0;
 bottom: 0;
 margin: auto;
  50px;
 height: 20px;
 text-align: center;
 line-height: 20px;
 }

1、盒子居中；

.add-link-tips{position: absolute;left: 0;right: 0;top: 0;bottom: 0;

.add-link-tips{position: absolute;left: 0;right: 0;top: 0;bottom: 0;
 margin: auto; 150px;height: 85px;background-color: #000000;
color: #fff;font-size: 14px;border-radius: 5px;box-shadow: #757b7f 0px 0px 5px;z-index: 2;opacity: 0.5;text-align: center;}