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<!DOCTYPE html>
<html>
<head>
<style>
div
{
background-color:red;
opacity:0.5;
filter:Alpha(opacity=50); /* IE8 and earlier */
}
</style>
</head>
<body>
<div>这个元素的不透明度是0.5!注意，文本和背景颜色都受到不透明度级别的影响!</div>
</body>
</html>