简单的说就是使用rgba的写法，如例所示：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>文字透明，背景不透明</title>
<style>
.div1{width:293px;height:219px;background:url(1.jpg) no-repeat;}
.div2{width:293px;height:100px;background:rgba(255,0,0,0.5);text-align: center;font-family:"Microsoft Yahei";font-size: 30px;color:#fff;}
</style>
</head>
<body>
<div class="div1">
<div class="div2">中华人民共和国万岁</div>
</div>
</body>
</html>
