.back-top {
  position: fixed;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 98rpx;
  height: 98rpx;
  background: #fff;
  border-radius: 50%;
  box-shadow: 0 0 12rpx rgba(111, 111, 111, 0.15);
  opacity: 1;
  transition: opacity 300ms linear;
}

.back-top-hide {
  opacity: 0;
}