html - CSS:类似于将元素的框阴影放置在与元素不同的 z-index 处的效果

Question

我有一个包含图像的容器和一个面板，当您将鼠标悬停在该图像上时会出现该面板。我试图让面板上的框阴影出现在图像后面，而面板的其余部分与图像重叠。

What I have vs. What I'd like to have

HTML:

<div class="container">
  <img class="icon" src="http://placehold.it/350x350" />
  <div class="sum-container left">
    <img src="http://placehold.it/350x150" />
  </div>
</div>

CSS:

.container .sum-container {
    position: absolute;
    top: 0;
    bottom: 0;
    border: solid 5px blue;
    background-color: white;
    width: 250px;
    height: 200px;
    max-height: 100%;
    opacity: 0;
    overflow: hidden;
    z-index: 5;
    pointer-events: none;
    transition-property: opacity;
    transition-duration: .250s;
}

.container .sum-container.left {
    right: 100%;
    margin-right: -5px;
    border-right: none;
    padding-right: 0px;
    box-shadow: 5px 5px 0px #888888;
}

.container .icon:hover + .sum-container {
    z-index: 6;
    opacity: 1;
}

.container {
  position: absolute;
  left: 300px;
  top: 20px;
}

.container img {
  width: 100%;
}

.icon {
    margin-left: auto;
    margin-right: auto;
    display: block;
    width: 100%;
    height: auto;
    max-width: 480px;
    background-color: blue;
    box-shadow: 5px 5px 0px #888888;
    text-align: center;
    font-size: 26px;
    color: white;
    text-decoration: none;
    padding: 5px;
    cursor: pointer;
    border: none;
    outline: none;
    user-drag: none;
}

我添加了一个 JSFiddle

此外，这里还是新的。如果有人可以建议更好的标题，请告诉我。我知道您实际上不能为一个元素设置多个 z-index，但我正在寻找具有类似效果的解决方案。

Answer 1

如果我理解最终目标，您可以使阴影成为具有负 z-index 的伪元素，并从 .sum 中删除 z-index -container 和 .sum-container 将在 .icon 之上，它的伪元素将在它们之下。

.container .sum-container {
    position: absolute;
    top: 0;
    bottom: 0;
    border: solid 5px blue;
    background-color: white;
    width: 250px;
    height: 200px;
    max-height: 100%;
    opacity: 1;
    pointer-events: none;
    transition-property: opacity;
    transition-duration: .250s;
}

.sum-container:after {
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  content: '';
  background: #888;
  transform: translate(0,10px);
  z-index: -1;
}

.container .sum-container.left {
    right: 100%;
    margin-right: -5px;
    border-right: none;
    padding-right: 0px;
}

.container .icon:hover + .sum-container {
    opacity: 1;
}

.container {
  position: absolute;
  left: 300px;
  top: 20px;
}

.container img {
  width: 100%;
}

.icon {
    margin-left: auto;
    margin-right: auto;
    display: block;
    width: 100%;
    height: auto;
    max-width: 480px;
    background-color: blue;
    box-shadow: 5px 5px 0px #888888;
    text-align: center;
    font-size: 26px;
    color: white;
    text-decoration: none;
    padding: 5px;
    cursor: pointer;
    border: none;
    outline: none;
    user-drag: none;
}

<div class="container">
  <img class="icon" src="http://placehold.it/350x350" />
  <div class="sum-container left">
    <img src="http://placehold.it/350x150" />
  </div>
</div>