animate.css/source/attention_seekers/jello.css

@keyframes jello {
  from, 11.1%, to {
    transform: none;
  }

  22.2% {
    transform: skewX(-12.5deg) skewY(-12.5deg);
  }

  33.3% {
    transform: skewX(6.25deg) skewY(6.25deg);
  }

  44.4% {
    transform: skewX(-3.125deg) skewY(-3.125deg);
  }

  55.5% {
    transform: skewX(1.5625deg) skewY(1.5625deg);
  }

  66.6% {
    transform: skewX(-0.78125deg) skewY(-0.78125deg);
  }

  77.7% {
    transform: skewX(0.390625deg) skewY(0.390625deg);
  }

  88.8% {
    transform: skewX(-0.1953125deg) skewY(-0.1953125deg);
  }
}

.jello {
  animation-name: jello;
  transform-origin: center;
}