<html>
<head>
<style type="text/css">
#sidebar p {
font-family: Verdana;
font-size: .9em; }
#sidebar .intro {
font-family: Georgia;
font-size: 1.25em;
color:red;
}
</style>
</head>
<body>
<div id=”sidebar”>
<p class=”intro”>
As you can see, the more CSS styles you create, the greater the potential for formatting
snafus. For example, you may create a class style specifying a particular
font and font size, but when you apply the style to a paragraph, nothing happens!
This kind of problem is usually related to the cascade. Even though you may think
that directly applying a class to a tag should apply the class’s formatting properties,
it may not if there’s a style with greater specificity.
You have a couple of options for dealing with this kind of problem. First, you can
use !important (as described in the box above) to make sure a property always
applies. The !important approach is a bit heavy handed, though, since it’s hard to
predict that you’ll never, ever, want to overrule an !important property someday.
Read on for two other cascade-tweaking solutions.
</p>
</div>
</body>
</html>
#sidebar P 样式的特异性为 101(ID 为 100，标记为 1选择器(，而 .intro 样式的特异性为 10(类选择器为 10 分(。由于 101 大于 10，因此 #sidebar p 优先。将 .intro 更改为 #sidebar .intro 会将其特异性更改为 110。
即使我改变了这个，我的结果也没有到来
谁能解释我。
输出：应为红色，字体大小为 1.25em，字体系列 -格鲁吉亚
ID sidebar 和 classname intro 两边的引号无效。 ”sidebar”应该是"sidebar".
浏览器将ID解释为”sidebar”而不是sidebar，因此，您的任何规则都不匹配。