body img {
  width: 100%;
}
body .middle {
  width: 100%;
  height: 3.65rem;
  position: relative;
  overflow: hidden;
}
body .middle img {
  position: absolute;
  width: 100%;
}
body .middle video {
  position: relative;
  display: block;
  z-index: 9;
  width: 3.13rem;
  height: 1.76rem;
  margin: 0.65rem auto 0;
}
body .btn {
  position: fixed;
  left: 0;
  bottom: 0;
  z-index: 999;
}