.shake {
  animation: shake 0.5s ease-in-out infinite;
  display: inline-block; /* 保证transform生效 */
}

@keyframes shake {
  0%, 100% { transform: translateY(0); }
  25% { transform: translateY(-2px); }
  50% { transform: translateY(2px); }
  75% { transform: translateY(-2px); }
}