css实现全屏遮罩，显示点击放大的图片，并有关闭按钮（x）

.bigPicBox {
  position: fixed;
  top: -150px;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.5);
  z-index: 9999;
  padding-bottom: 150px;
  .bigPic {
    position: relative;
    margin: auto;
    margin-top: 285px;
    z-index: 9999;
    width: 900px;
    height: 500px;
    i {
      width: 19px;
      height: 19px;
      color: #fff;
      position: absolute;
      top: 15px;
      right: 15px;
      z-index: 9999;
      cursor: pointer;
    }
    img {
      width: 100%;
      height: 100%;
    }
  }
}