/* spec 7.1., 7.2. */
:root {
  --transition-duration: 100ms;
  --transition-easing: ease-out;
}

/* spec 14.29., 39.16. */
@keyframes shake {
  0%, 100% { left: 0; }
  14.29%, 42.86%, 71.43% { left: -3px; }
  28.57%, 57.14%, 85.71% { left: 3px; }
}