代码示例:(标识:css_background_opacity_1)
<!DOCTYPE html>
<html>
<head>
<style>
div {
  background-color: green;
}

div.first {
  opacity: 0.1;
}

div.second {
  opacity: 0.3;
}

div.third {
  opacity: 0.6;
}
</style>
</head>
<body>

<h1>透明框</h1>

<p>当使用 opacity 属性为元素背景添加透明度时,其所有子元素也会变为透明。这可能会使完全透明的元素内的文本难以阅读:</p>

<div class="first">
  <h1>opacity 0.1</h1>
</div>

<div class="second">
  <h1>opacity 0.3</h1>
</div>

<div class="third">
  <h1>opacity 0.6</h1>
</div>

<div>
  <h1>opacity 1(默认)</h1>
</div>

</body>
</html>
运行结果: