span {

  display: inline-block;
}

span.constant-tilt-shake {
  animation: tilt-shaking 0.3s infinite;
}

@keyframes tilt-shaking {
  0% { transform: rotate(0deg); }
  25% { transform: rotate(2deg); }
  50% { transform: rotate(0eg); }
  75% { transform: rotate(-2deg); }
  100% { transform: rotate(0deg); }
}