.github-corner:hover .octo-arm {
  animation: octocat-wave 560ms ease-in-out;
}
@keyframes octocat-wave {
  0%, 100% { transform: rotate(0); }
  20%, 60% { transform: rotate(-25deg); }
  40%, 80% { transform: rotate(10deg); }
}
@media (max-width:500px) {
  .github-corner:hover .octo-arm { animation: none; }
  .github-corner .octo-arm { animation: octocat-wave 560ms ease-in-out; }
}