使用CSS动画和关键帧的类似gmail的加载

Question

我正在尝试复制gmail加载动画。我从当前的加载元素开始，它仅通过CSS动画和HTML完成。 徽标既不是SVG路径，也巧妙地使用了animation和keyframes。 CSS动画代码是如何组装的？我认为很难理解这是通过编程方式还是通过某种工具完成的。

$('#loading').show()

body {
  margin: 0;
  width: 100%;
  height: 100%
}

body,
td,
input,
textarea,
select,
#loading {
  font-family: arial, sans-serif
}

input,
textarea,
select {
  font-size: 100%
}

#loading {
  position: absolute;
  width: 100%;
  height: 100%;
  z-index: 1000;
  background-color: #fff
}

.msg {
  color: #757575;
  font-size: 20px;
  letter-spacing: .2px;
  line-height: 20px;
  text-align: center
}

#nlpt {
  animation: a-s .5s 2.5s 1 forwards;
  background-color: #f1f1f1;
  height: 4px;
  margin: 56px auto 20px;
  opacity: 0;
  overflow: hidden;
  position: relative;
  width: 300px
}

#nlpt::before {
  animation: a-lb 20s 3s linear forwards;
  background-color: #db4437;
  content: '';
  display: block;
  height: 100%;
  position: absolute;
  transform: translateX(-300px);
  width: 100%
}

@keyframes a-lb {
  0% {
    transform: translateX(-300px)
  }
  5% {
    transform: translateX(-240px)
  }
  15% {
    transform: translateX(-30px)
  }
  25% {
    transform: translateX(-30px)
  }
  30% {
    transform: translateX(-20px)
  }
  45% {
    transform: translateX(-20px)
  }
  50% {
    transform: translateX(-15px)
  }
  65% {
    transform: translateX(-15px)
  }
  70% {
    transform: translateX(-10px)
  }
  95% {
    transform: translateX(-10px)
  }
  100% {
    transform: translateX(-5px)
  }
}

@keyframes a-s {
  100% {
    opacity: 1
  }
}

@keyframes a-h {
  100% {
    opacity: 0
  }
}

@keyframes a-nt {
  100% {
    transform: none
  }
}

@keyframes a-e {
  43% {
    animation-timing-function: cubic-bezier(.8, 0, .2, 1);
    transform: scale(.75)
  }
  60% {
    animation-timing-function: cubic-bezier(.8, 0, 1, 1);
    transform: translateY(-16px)
  }
  77% {
    animation-timing-function: cubic-bezier(.16, 0, .2, 1);
    transform: none
  }
  89% {
    animation-timing-function: cubic-bezier(.8, 0, 1, 1);
    transform: translateY(-5px)
  }
  100% {
    transform: none
  }
}

@keyframes a-ef {
  24% {
    animation-timing-function: cubic-bezier(.8, 0, .6, 1);
    transform: scaleY(.42)
  }
  52% {
    animation-timing-function: cubic-bezier(.63, 0, .2, 1);
    transform: scaleY(.98)
  }
  83% {
    animation-timing-function: cubic-bezier(.8, 0, .84, 1);
    transform: scaleY(.96)
  }
  100% {
    transform: none
  }
}

@keyframes a-efs {
  24% {
    animation-timing-function: cubic-bezier(.8, 0, .6, 1);
    opacity: .3
  }
  52% {
    animation-timing-function: cubic-bezier(.63, 0, .2, 1);
    opacity: .03
  }
  83% {
    animation-timing-function: cubic-bezier(.8, 0, .84, 1);
    opacity: .05
  }
  100% {
    opacity: 0
  }
}

@keyframes a-es {
  24% {
    animation-timing-function: cubic-bezier(.8, 0, .6, 1);
    transform: rotate(-25deg)
  }
  52% {
    animation-timing-function: cubic-bezier(.63, 0, .2, 1);
    transform: rotate(-42.5deg)
  }
  83% {
    animation-timing-function: cubic-bezier(.8, 0, .84, 1);
    transform: rotate(-42deg)
  }
  100% {
    transform: rotate(-43deg)
  }
}

.invfr {
  position: absolute;
  left: 0;
  top: 0;
  z-index: -1;
  width: 0;
  height: 0;
  border: 0
}

.msgb {
  position: absolute;
  right: 0;
  font-size: 12px;
  font-weight: normal;
  color: #000;
  padding: 20px
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="loading" style="display:none">
  <div style="bottom:0;left:0;overflow:hidden;position:absolute;right:0;top:0">
    <div style="animation:a-h .5s 1.25s 1 linear forwards,a-nt .6s 1.25s 1 cubic-bezier(0,0,.2,1);background:#eee;border-radius:50%;height:800px;left:50%;margin:-448px -400px 0;position:absolute;top:50%;transform:scale(0);width:800px"></div>
  </div>
  <div style="height:100%;text-align:center">
    <div style="height:50%;margin:0 0 -140px"></div>
    <div style="height:128px;margin:0 auto;position:relative;width:176px">
      <div style="animation:a-s .5s .5s 1 linear forwards,a-e 1.75s .5s 1 cubic-bezier(0,0,.67,1) forwards;opacity:0;transform:scale(.68)">
        <div style="background:#ddd;border-radius:12px;box-shadow:0 15px 15px -15px rgba(0,0,0,.3);height:128px;left:0;overflow:hidden;position:absolute;top:0;transform:scale(1);width:176px">
          <div style="animation:a-nt .667s 1.5s 1 cubic-bezier(.4,0,.2,1) forwards;background:#d23f31;border-radius:50%;height:270px;left:88px;margin:-135px;position:absolute;top:25px;transform:scale(.5);width:270px"></div>
          <div style="height:128px;left:20px;overflow:hidden;position:absolute;top:0;transform:scale(1);width:136px">
            <div style="background:#e1e1e1;height:128px;left:0;position:absolute;top:0;width:68px">
              <div style="animation:a-h .25s 1.25s 1 forwards;background:#eee;height:128px;left:0;opacity:1;position:absolute;top:0;width:68px"></div>
            </div>
            <div style="background:#eee;height:100px;left:1px;position:absolute;top:56px;transform:scaleY(.73)rotate(135deg);width:200px"></div>
          </div>
          <div style="background:#bbb;height:176px;left:0;position:absolute;top:-100px;transform:scaleY(.73)rotate(135deg);width:176px">
            <div style="background:#eee;border-radius:12px 12px 0 0;bottom:117px;height:12px;left:55px;position:absolute;transform:rotate(-135deg)scaleY(1.37);width:136px"></div>
            <div style="background:#eee;height:96px;position:absolute;right:0;top:0;width:96px"></div>
            <div style="box-shadow:inset 0 0 10px #888;height:155px;position:absolute;right:0;top:0;width:155px"></div>
          </div>
          <div style="animation:a-s .167s 1.283s 1 linear forwards,a-es 1.184s 1.283s 1 cubic-bezier(.4,0,.2,1) forwards;background:linear-gradient(0,rgba(38,38,38,0),rgba(38,38,38,.2));height:225px;left:0;opacity:0;position:absolute;top:0;transform:rotate(-43deg);transform-origin:0 13px;width:176px"></div>
        </div>
        <div style="animation:a-ef 1.184s 1.283s 1 cubic-bezier(.4,0,.2,1) forwards;border-radius:12px;height:100px;left:0;overflow:hidden;position:absolute;top:0;transform:scaleY(1);transform-origin:top;width:176px">
          <div style="height:176px;left:0;position:absolute;top:-100px;transform:scaleY(.73)rotate(135deg);width:176px">
            <div style="animation:a-s .167s 1.283s 1 linear forwards;box-shadow:-5px 0 12px rgba(0,0,0,.5);height:176px;left:0;opacity:0;position:absolute;top:0;width:176px"></div>
            <div style="background:#ddd;height:176px;left:0;overflow:hidden;position:absolute;top:0;width:176px">
              <div style="animation:a-nt .667s 1.25s 1 cubic-bezier(.4,0,.2,1) forwards;background:#db4437;border-radius:50%;bottom:41px;height:225px;left:41px;position:absolute;transform:scale(0);width:225px"></div>
              <div style="background:#f1f1f1;height:128px;left:24px;position:absolute;top:24px;transform:rotate(90deg);width:128px"></div>
              <div style="animation:a-efs 1.184s 1.283s 1 cubic-bezier(.4,0,.2,1) forwards;background:#fff;height:176px;opacity:0;transform:rotate(90deg);width:176px"></div>
            </div>
          </div>
        </div>
      </div>
    </div>
    <div id="nlpt"></div>
    <div style="animation:a-s .25s 1.25s 1 forwards;opacity:0" class="msg">Loading Gmail…</div>
  </div>
</div>

这是复制它的jsFiddle。