在全页面居中

     .redPackets-box {
        position: absolute;
        top: 50%;
        left: 50%;
        -webkit-transform: translate3d(-50%, -50%, 0);
        transform: translate3d(-50%, -50%, 0);
        .redPackets {
          width: 200px;
          height: 200px;
          animation: bounce 0.8s ease-out;
        }
      }