蒙板

蒙板

<div class="container">
    <div class="dialog">
      <div class="contain">大家好</div>
    </div>
</div>

.container {
      position: fixed;
      top: 0;
      left: 0;
      bottom: 0;
      right: 0;
      background-color: rgba(0,0,0,.5);
      overflow: auto;
      white-space: nowrap;
      text-align: center;
      font-size: 0;
}
.container::after {
      content: '';
      display: inline-block;
      height: 100%;
      vertical-align: middle;
}
.dialog {
      display: inline-block;
      vertical-align: middle;
      text-align: center;
      font-size: 14px;
      white-space: normal;
}
.contain {
      width: 520px;
      height: 300px;
      background-color: #fff;
      line-height: 300px;
}