SVG动态背景

这是我参与11月更文挑战的第10天，活动详情查看：11月更文挑战

<svg viewBox="0 0 100 100" preserveAspectRatio="xMidYMid slice">
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        <animate attributeName="fx" dur="34s" values="0%;3%;0%" repeatCount="indefinite" />
        <stop offset="0%" stop-color="#ff0" />
        <stop offset="100%" stop-color="#ff00" />
      </radialGradient>
       <radialGradient id="Gradient2" cx="50%" cy="50%" fx="10%" fy="50%" r=".5">
        <animate attributeName="fx" dur="23.5s" values="0%;3%;0%" repeatCount="indefinite" />
        <stop offset="0%" stop-color="#0ff" />
        <stop offset="100%" stop-color="#0ff0" />
      </radialGradient>
      <radialGradient id="Gradient3" cx="50%" cy="50%" fx="50%" fy="50%" r=".5">
        <animate attributeName="fx" dur="21.5s" values="0%;3%;0%" repeatCount="indefinite" />
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    </rect>
  </svg>
<div class="child">
Clouds<br /> of  ther.</div>

@import url("https://fonts.googleapis.com/css?family=Libre+Franklin:400,700&subset=latin");
html {
  width: 100%;
  height: 100%;
  box-sizing: border-box;
  background: #fff;
}

*,
*:before,
*:after {
  box-sizing: inherit;
}

body {
  width: 100%;
  height: 100%;
  font: 100px/100px "Libre Franklin";
  font-weight: 900;
  color: white;
  -webkit-font-smoothing: antialiased;
  font-smoothing: antialiased;
  overflow: hidden;
}

.child {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  letter-spacing: -5px;
  mix-blend-mode: overlay;
  text-shadow: 0 0 5px #fff;
  color: #fff6;
}

svg {
  position: absolute;
  top: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
}