DIV内容垂直居中

<style>

#wrapper {
  display: table;
  width: 100%;
  height: 100%;
  background: #000;
  margin: 0 auto;
  color: red;
}
#cell {
  display: table-cell;
  vertical-align: middle;
}
</style>


<template>
  <div id="wrapper">
    <div id="cell">
      <img id="img_heard">
      <span id="lb_top">后台管理中心</span>
      <el-button type="danger" icon="el-icon-close" id="btn_exit" size="small">退出登录</el-button>
    </div>
  </div>
</template>