示例代码： jsfiddle/RuQNP/
<！DOCTYPE html> < html> < head> < title> Foo< / title> < style type =text / css> a：link，a：visited { color：blue; } a：hover，a：active { color：red; } .foo a：link，.foo a：visited { color：green; } / *可能的修复程序* / / * .foo a：hover，.foo a：active { color：red; } * / < / style> < / head> < body> < div class =foo> < a href =example/>示例< / a> < / div> < / body> < / html>我预期的：
悬停时链接会显示为红色。
我得到了什么：
悬停时链接显示为绿色。
问题：
如果我理解 www.w3/TR/CSS21/cascade.html#specificity （感谢，BoltClock），这是代码中各种选择器的特异性表。
a：link - 0 0 1 1 a：visited - 0 0 1 1 a：hover - 0 0 1 1 a：active - 0 0 1 1 .foo a：link - 0 0 2 1 .foo a：visited - 0 0 2 1 pre>因此，为 .foo a：link 定义的样式覆盖当链接以及 hover 伪类应用于A时，a：hover 同样，为 .foo定义的样式a：访问的 访问以及时，覆盖 a：hover 的样式c> hover 伪类应用于 foo 的A元素。
解决方案当您第一次使用CSS时，您可能已经了解了LoVe-HAte助记符，用于指定链接选择器的顺序（ a：link ， a：visited ， a：hover ， a：active ）。你是否曾经想过为什么选择这个助记符？
那么， spec 了解当使用所有规则应用于同一元素时如何处理链接和动态伪类，这解释了为什么你需要按照以下顺序设置链接选择器：
请注意，A：悬停必须放置在A：链接和A： ，因为否则级联规则将隐藏A：hover规则的'color'属性。类似地，因为A：active放置在A：hover之后，当用户激活并悬停在A元素上时，将应用活动颜色（lime）。
无论如何，我试图在上面的点是所有四个伪类，作为伪类，具有相等的特异性。关于特殊性的一切都适用。在这种情况下，在一组同样特定的选择器中，应用最后一个规则。
现在，简单介绍 .foo 选择器会导致您的第二组链接/访问规则覆盖您的第一组链接/访问样式和悬停/活动样式，强制该类的元素中的链接始终显示为绿色，直到您添加悬停/ 对不起，如果我的答案似乎缝合或slipshod的方式，我现在在我的iPhone上打字，这是很难想到这里...
Sample code: jsfiddle/RuQNP/
<!DOCTYPE html> <html> <head> <title>Foo</title> <style type="text/css"> a:link, a:visited { color: blue; } a:hover, a:active { color: red; } .foo a:link, .foo a:visited { color: green; } /* A possible fix */ /* .foo a:hover, .foo a:active { color: red; } */ </style> </head> <body> <div class="foo"> <a href="example/">Example</a> </div> </body> </html>What I was expecting:
The link would appear red on hover.
What I get:
The link appears green on hover.
Questions:
If I understand www.w3/TR/CSS21/cascade.html#specificity properly (Thanks, BoltClock), this is the specificity table for the various selectors in the code.
a:link - 0 0 1 1 a:visited - 0 0 1 1 a:hover - 0 0 1 1 a:active - 0 0 1 1 .foo a:link - 0 0 2 1 .foo a:visited - 0 0 2 1So, the style defined for .foo a:link overrides the style for a:hover when both link as well as hover pseudo-classes apply to an A element of class foo.
Similarly, the style defined for .foo a:visited overrides the style for a:hover when both visited as well as hover pseudo-classes apply to an A element of class foo.
解决方案When you first started with CSS, you might have learned about the LoVe-HAte mnemonic for the order in which to specify link selectors (a:link, a:visited, a:hover, a:active). Have you ever wondered why this mnemonic was chosen?
Well, there's a note in the spec on how the link and dynamic pseudo-classes are treated when multiple rules using all of them apply to the same element, which explains why you need to set link selectors in that order:
Note that the A:hover must be placed after the A:link and A:visited rules, since otherwise the cascading rules will hide the 'color' property of the A:hover rule. Similarly, because A:active is placed after A:hover, the active color (lime) will apply when the user both activates and hovers over the A element.
Anyway, the point I'm trying to make above is that all four pseudo-classes, being pseudo-classes, have equal specificity. Everything else about specificity applies. In this case, out of a bunch of equally specific selectors, the last rule is applied. When or how each pseudo-class is triggered is never relevant.
Now, the simple introduction of the .foo selector causes your second set of link/visited rules to override your first set of link/visited styles and the hover/active styles, forcing links in elements with that class to always appear green until you add hover/active styles with the .foo selector.
Sorry if my answer seems stitched-up or slipshod by the way, I'm typing this on my iPhone right now and it's pretty hard to think out here...
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