CSS 计算样式

    bottom: 40px;
    height: calc(100% - 90px);

控制图片居中

    font-family: Arial, sans-serif;
    font-size: 16px;
    background-color: rgba(51, 51, 51, 0.95);
    height: 100%;
    position: fixed;  -------主要
    top: 34px;
    left: 0;
    right: 0;
    z-index: 101;

position: relative;
    display: inline-block;
    vertical-align: middle;  ---主要

 转: https://www.cnblogs.com/bigqipa/p/7976028.html