代码示例:(标识:css3_gradient-linear_rainbow)
<!DOCTYPE html>
<html>
<head>
<style>
#grad1 {
  height: 55px;
  background-color: red; /* 针对不支持渐变的浏览器 */
  background-image: linear-gradient(to right, red, orange, yellow, green, blue, indigo, violet);
}
</style>
</head>
<body>

<div id="grad1" style="text-align:center;margin:auto;color:#888888;font-size:40px;font-weight:bold">
彩虹背景
</div>

</body>
</html>
运行结果: