为什么这个伪 class 选择器不起作用？

Question

I'm trying to use:after selector to draw a inside-border in every div I hover. Now the ":after" pseudo class doesn't work?我正在尝试使用:after 选择器在每个 div I hover 中绘制一个内边框。现在“:after”伪 class 不起作用？ any idea why this selector doesn't work?知道为什么这个选择器不起作用吗？ if I just use the:hover pseudo class works, the thing is that I want to use both classes!如果我只使用：hover 伪 class 作品，问题是我想同时使用这两个类！

Have a look at this EX看看这个EX

thanks!谢谢！

<body>
    <h1>Example Six</h1>
                
    <p>Grade: A</p>
    <p>this is the thing</p>

    <div class="w3c">
        <div id="tab16">
            <a href="#tab16">cars</a>
            
            <div class="test">
                <div><img alt="" src="http://placehold.it/176x106/" /></div>
            </div>                    
        </div> <!-- ends tab16 -->        
        <div id="tab17">
            <a href="#tab17">othercars</a>
        <div>
            <div><img alt="" src="http://placehold.it/180x110/" /></div>
            <div><img alt="" src="http://placehold.it/180x110/" /></div>
        </div>
    </div> <!-- ends .w3c -->
</body>

The css: css：

@charset "utf-8";
/* CSS Document */
    
.w3c {
    min-height: 250px;
    position: relative;
    width: 554px;
}
.w3c > div {
    display: inline;
}
.w3c > div > a {
    margin-left: -1px;
    position: relative;
    left: 1px;
    text-decoration: none;
    color: #fff;
    background: #666666;
    display: block;
    float: left;
    padding: 5px 10px;
    border: 1px solid #ccc;
    border-bottom: 1px solid white;
}
.w3c > div:not(:target) > a {
    border-bottom: 0;
    background: #b0b0b0;
    /*-moz-linear-gradient(top, white, #eee); */
}   
.w3c > div:target > a {
    background: white;
    color: #b0b0b0;
}
                
.w3c > div > div {
    background: white;
    z-index: 0;
    left: 0;
    top: 30px;
    bottom: 0;
    right: 0;
    padding: 10px;
    border: 1px solid #ccc;
    width: 596px;
    height: 133px;
}   
.w3c  div  div > div {
    border: 1px solid red;
    float: left;
    width: 180px;
    height:110px;
    margin-left: 10px;
}
.w3c  div div > div:hover:after {
    border: 1px solid black;
    width:178px;
    height: 108px;
}
            
/* .w3c > div > div > a  > img:after {
    border: 2px solid black;
    width:178;
    height: 108px;
} */
.w3c > div:not(:target) > div {
    position: absolute;
}
.w3c > div:target > div {
    position: absolute;
    z-index: 1;
}

Answer 1

For the :after pseudo-element to show up you need to give it content and display it as a block.要显示:after伪元素，您需要为其提供内容并将其显示为块。

Then, absolutely position the :after and relatively position the div itself:然后，绝对 position :after和相对 position div本身：

.w3c div div > div {
    position: relative;
    border: 1px solid red;
    float: left;
    width: 180px;
    height: 110px;
    margin-left: 10px;
}

.w3c div div > div:hover:after {
    display: block;
    content: '';
    position: absolute;
    border: 1px solid black;
    width: 178px;
    height: 108px;
}

Answer 2

I've found out what the problem is.我发现了问题所在。

::after is used to add content after an existing element, not to style elements that come after things. ::after用于在现有元素之后添加内容，而不是为事物之后的元素设置样式。

You might want to use nth-child() to target the x elements, or every x element.您可能希望使用nth-child()来定位 x 元素或每个 x 元素。

.w3c div div > div:nth-child(2):hover {
     border: 1px solid black;
}

http://css-tricks.com/how-nth-child-works/ http://css-tricks.com/how-nth-child-works/

为什么这个伪 class 选择器不起作用？

问题描述

2 个解决方案

解决方案1
3 已采纳 2012-02-13 14:32:52

解决方案2
0 2012-02-13 14:45:58

为什么这个伪 class 选择器不起作用？

问题描述

2 个解决方案

解决方案1 3 已采纳 2012-02-13 14:32:52

解决方案2 0 2012-02-13 14:45:58

解决方案1
3 已采纳 2012-02-13 14:32:52

解决方案2
0 2012-02-13 14:45:58