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问题:

below is my markup. when i move the mouse over the hyperlinks they get underlined and turn red. but if i swap the order of the last two rules, the hyperlinks still get underlined, but their color changes to black rather than red. is this by design? if so, how are the rules applied?

thanks! konstantin


<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
    <title>
    <style type="text/css" media="all">
        .menu a
        {
            text-decoration: none;
        }
        .menu li:hover a
        {
            color: black;
        }
        .menu li a:hover
        {
            color: red;
            text-decoration: underline;
        }
    </style>
</head>
<body>
    <div class="menu">
        <ul>
            <li><a href="#">item0</a></li>
            <li><a href="#">item1</a></li>
        </ul>
    </div>
</body>
</html>

回答1:

If the rules are equal in specificity (in this case they are), individual rules get overridden in the order they're defined in the CSS, so in your example red wins because it comes later in the CSS definitions. The same rule applies in other cases as well, for example:

<div class="red green">

Which of these wins?

.green { color: green; }
.red { color: red; }

.red wins here, it doesn't matter the order in the class attribute, all that matters is the order the styles are defined in the CSS itself.

回答2:

Consider the following HTML.

<div class="red">
    Some red text...
</div>

And this CSS..

.red {color: red}
.red {color: blue}
.red {color: yellow}

You guessed it, the text will be yellow!

回答3:

Yes the order matters, and in this case it is not really the order which is why you are having the same result regardless of the order.

The .menu li:hover a is applied to the li, which is a parent of the a and the hover is not applied to the a it is applied to the li.

The .menu li a:hover is applied to the a.

Regardless of the order the .menu li a:hover style will be applied to the a.

The better way to handle that is to have the hover pseudo selector applied to only the a element and make set display: block on it, with height and width set to 100%. This will fill the entire LI

Hope this clarifies things.

回答4:

Yes, it does. The last point of the cascading order reads:

Finally, sort by order specified: if two declarations have the same weight, origin and specificity, the latter specified wins. Declarations in imported style sheets are considered to be before any declarations in the style sheet itself.

回答5:

CSS rules are applied in order if they have the same specificity. In your case, they do, so order matters.

With the order you have in your question, the rules apply text-decoration: none. The second and third rules causes hovering the mouse over the link to modify those two styles in order because the a tag is inside the li tag. First, the color turns black; then, the color turns red and the underline appears.

Reverse the order of the last two rules like so:

    .menu a
    {
        text-decoration: none;
    }
    .menu li a:hover
    {
        color: red;
        text-decoration: underline;
    }
    .menu li:hover a
    {
        color: black;
    }

Now, the text-decoration: none gets applied as before. Then, upon mouse-over, the first rule changes the color to red and adds an underline, followed by the color changing to black.