Css3 Animation 动画原则四

<h1>Principle 4: Straight Ahead Action and Pose to Pose</h1>
<h2><a href="https://cssanimation.rocks/principles/" target="_parent">Animation Principles for the Web</h2>
<article class="principle four">
    <div class="shape a"></div>
    <div class="shape b"></div>
</article>

.four .shape.a {
    left: calc(50% - 8em);
    animation: four 6s infinite cubic-bezier(.57,-0.5,.43,1.53);
}

.four .shape.b {
  left: calc(50% + 8em);
  animation: four 6s infinite steps(1);
}

@keyframes four {
  0%, 10% {
    transform: none;
  }
  26%, 30% {
    transform: rotateZ(-45deg) scale(1.25);
  }
  40% {
    transform: rotateZ(-45deg) translate(2em, -2em) scale(1.8);
  }
  50%, 75% {
    transform: rotateZ(-45deg) scale(1.1);
  }
  90%, 100% {
    transform: none;
  }
}

/* General styling */
body {
  margin: 0;
  background: #e9b59f;
  font-family: HelveticaNeue, Arial, Sans-serif;
  color: #fff;
}

h1 {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  text-align: center;
  font-weight: 300;
}

h2 {
  font-size: 0.75em;
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  text-align: center;
}

a {
  text-decoration: none;
  color: #333;
}

.principle {
  width: 100%;
  height: 100vh;
  position: relative;
}

.shape {
  background: #2d97db;
  border: 1em solid #fff;
  width: 4em;
  height: 4em;
  position: absolute;
  top: calc(50% - 2em);
  left: calc(50% - 2em);
}