element()

element(id)

<div id="target-box">
  <p>这个盒子使用 ID 为 #my-background 的元素作为其背景！</p>
</div>

<div id="background-container">
  <div id="my-background">
    <p>这段文字是背景的一部分。很酷吧？</p>
  </div>
</div>

#target-box {
  width: 400px;
  height: 400px;
  background: -moz-element(#my-background) no-repeat;
}

#background-container {
  overflow: hidden;
  height: 0;
}

#my-background {
  width: 1024px;
  height: 1024px;
  background-image: linear-gradient(to right, red, orange, yellow, white);
}

#my-background p {
  transform-origin: 0 0;
  rotate: 45deg;
  color: white;
}

<div id="css-source">
  <h1>页面预览</h1>
</div>
<div id="css-result"></div>

#css-result {
  background: -moz-element(#css-source) no-repeat;
  width: 256px;
  height: 32px;
  background-size: 80%;
  border: dashed;
}