1.CLASS和ID的优先级比较.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<title>无标题 1</title>
<style type="text/css">
.a h1{
color:fuchsia;
}
.b h1{
color:lime;
}
#a h1{
color:fuchsia;
}
#b h1{
color:lime;
}
</style>
</head>
<body>
<div class="a">
<h1>CLASS在前</h1>
<div id="b">
<h1>ID在后</h1>
</div>
</div>
<div class="a">
<h1>CLASS在前</h1>
<div class="b">
<h1>CLASS在后</h1>
</div>
</div>
<div id="a">
<h1>ID在前</h1>
<div class="b">
<h1>CLASS在后</h1>
</div>
</div>
<div id="a">
<h1>ID在前</h1>
<div id="b">
<h1>ID在后</h1>
</div>
</div>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<title>无标题 1</title>
<style type="text/css">
.a h1{
color:fuchsia;
}
.b h1{
color:lime;
}
#a h1{
color:fuchsia;
}
#b h1{
color:lime;
}
</style>
</head>
<body>
<div class="a">
<h1>CLASS在前</h1>
<div id="b">
<h1>ID在后</h1>
</div>
</div>
<div class="a">
<h1>CLASS在前</h1>
<div class="b">
<h1>CLASS在后</h1>
</div>
</div>
<div id="a">
<h1>ID在前</h1>
<div class="b">
<h1>CLASS在后</h1>
</div>
</div>
<div id="a">
<h1>ID在前</h1>
<div id="b">
<h1>ID在后</h1>
</div>
</div>
</body>
</html>
结论:上面的代码说明了在CSS样式中ID的优先级别比CLASS要高.(IE 6 7 8 FF C结果一致)