:before/:after 伪元素的内容垂直居中

问题描述

我正在尝试实现类似于这张图片的效果:

我有一个包含在 div 中的图像(作为幻灯片的一部分)，并且使用 :before 和 :after 伪元素，我显示了两个控件以移动到下一个 (>>) 或上一个 (<<) 幻灯片的图像.

到目前为止，我有这个:

div {位置:相对；}div:之前{显示:块；高度:100%；内容:东西"；位置:绝对；顶部:0；左:0；文本对齐:居中；}

但是，我不能将伪元素的内容居中，文本显示如下:

这有可能实现吗?如果不是，最语义化的解决方法是什么?我不想将元素本身居中，而只是将其内容居中.我希望将元素拉伸到 100% 的高度.

http://jsfiddle.net/rdy4u/p>

Edit2:另外，img是liquid/fluid，div/img的高度未知，宽度设置为800px，max-width为80%.

假设你的元素不是 <img> (因为自闭合元素上不允许使用伪元素)，让我们假设它是一个 <div>，所以一种方法可能是:

div {高度:100 像素；行高:100px；}div:之前，div:之后{内容: "";...显示:内联块；垂直对齐:中间；高度: ...;行高:正常；}

如果你不能改变 div 的 line-height，另一种方法是:

div {位置:相对；}div:之前，div:之后{位置:绝对；显示:块；最高:50%；-webkit-transform: translateY(-50%);-moz 变换:翻译 Y(-50%)；-ms-transform: translateY(-50%);变换:translateY(-50%)；内容: "";宽度: ...}

否则，只需将指示器作为背景放置在中心位置.

I'm trying to achieve something similar to this picture:

I have an image (as part of a slideshow) wrapped in a div, and with :before and :after pseudo-elements, I display two controls to move onto the next (>>) or previous (<<) images of the slideshow.

So far, I have this:

div {
  position: relative;
}

div:before {
  display:block;
  height: 100%;
  content: "stuff";
  position:absolute;
  top: 0; left: 0;
  text-align: center;
}

I can't, however, center the content of the pseudo-elements, the text appears like this:

Is this possible to achieve? If not, what would be the most semantic workaround? I do not want to center the element itself, only its content. I'd prefer to have the element stretched to 100% height.

Edit: http://jsfiddle.net/rdy4u/

Edit2: Also, the img is liquid/fluid, the height of the div/img are unknown, and the width is set to 800px and max-width to 80%.

Assuming your element is not an <img> (because pseudo elements are not allowed on self-closing elements), let's suppose it's a <div>, so a way could be:

div {
    height: 100px ;
    line-height: 100px;
}
div:before, div:after {
    content: "";
    ...
    display: inline-block;
    vertical-align: middle;
    height: ...;
    line-height: normal;
}

If you cannot change the line-height of the div, another way is:

div {
    position: relative;
}
div:before, div:after {
    position: absolute;
    display: block;
    top: 50%;
    -webkit-transform: translateY(-50%);
    -moz-transform: translateY(-50%);
    -ms-transform: translateY(-50%);
    transform: translateY(-50%);
    content: "";
    width: ...
}

Otherwise, just place the indicators as a background in center position.

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