css - 为什么 webkit 过滤器悬停时堆叠顺序会发生变化？

Question

我注意到在应用 webkit 过滤器时我的堆叠顺序有一个奇怪的问题。为什么，当我将鼠标悬停在图像上时，堆叠顺序会发生变化？

我宁愿不必使用 z-indexing 来解决这个问题，因为它会破坏其他网站元素。

这是我的 JSFiddle http://jsfiddle.net/r13ycy1p/

请原谅荷马，我只需要一张图片。

编辑:如何反转效果以阻止绝对位置 div 被隐藏？

这是我的 HTML

<ul>
<li>
    <a href="#">
        <div class="slide-content">
            <div class="slide-title">
                <h1>hello world</h1>
            </div>
            <div class="slide-desc">
                <p>a description about something</p>
            </div>
        </div>
        <img src="http://img4.wikia.nocookie.net/__cb20130920142351/simpsons/images/e/e9/Pic_1187696292_8.jpg"/>

    </a>
</li>
</ul>

CSS

li {
list-style:none;    
}

.slide-content {
position:absolute;
color:red;
top:50px;
}

li a:hover img{
-webkit-filter: grayscale(100%); /* For Webkit browsers */
}

Answer 1

这是因为 none 以外的值建立了一个 stacking context .这记录在 spec 中(目前处于工作草案状态):

2 Module interactions

This specification defines a set of CSS properties that affect the visual rendering of elements to which those properties are applied; these effects are applied after elements have been sized and positioned according to the Visual formatting model from [CSS21]. Some values of these properties result in the creation of a containing block, and/or the creation of a stacking context.

规范还指出:

5 Graphic filters: the filter property

A computed value of other than none results in the creation of a stacking context [CSS21] the same way that CSS opacity does.