body {
  background-color: #000;
  overflow: hidden;
  position: relative;
}

body::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-image: url('https://xn--xu0a.cn/favicon.ico');
  animation: snowfall 10s linear infinite;
}

@keyframes snowfall {
  0% {
    transform: translateY(-100%);
  }
  100% {
    transform: translateY(100%);
  }
}