具有变换的元素内的子元素 z-index 属性

Question

我遇到了问题，我想知道你们是否可以帮助我解决这个问题。

如代码片段所示，我有一些元素

transform: translate(0,0);

然后，在它们内部，我有一个 "dropdown" 元素，当您单击按钮时会显示该元素。

当这个下拉列表的一部分隐藏在其他元素后面时，问题就来了，我发现这是因为它的父元素有这个转换属性。

我的代码有更多的东西，代码片段只是一个例子。我无法摆脱转换属性.

我想知道是否有任何解决方案。我正在尝试仅使用 CSS.

来解决它

干杯！！

$(document).ready(function() {
  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parent().find('.template-options-dropdown').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  transform: translate(0, 0);
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
}

.template-options-dropdown.open {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

Answer 1

z-index 仅适用于位置属性已明确设置为绝对、固定或相对的元素。因此，将 position: relative 应用于 li 元素。

对于固定数量的元素，可以试试

.boxes li:nth-child(1) {
  z-index: 8;
}

.boxes li:nth-child(2) {
  z-index: 7;
}

.boxes li:nth-child(3) {
  z-index: 6;
}

.boxes li:nth-child(4) {
  z-index: 5;
}

.boxes li:nth-child(5) {
  z-index: 4;
}

.boxes li:nth-child(6) {
  z-index: 3;
}

.boxes li:nth-child(7) {
  z-index: 2;
}

.boxes li:nth-child(8) {
  z-index: 1;
}

或者对于未知数量的元素，您可以使用脚本动态应用它。

$(document).ready(function() {
  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parent().find('.template-options-dropdown').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  transform: translate(0, 0);
  position: relative;
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
}

.template-options-dropdown.open {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

.boxes li:nth-child(1) {
  z-index: 8;
}

.boxes li:nth-child(2) {
  z-index: 7;
}

.boxes li:nth-child(3) {
  z-index: 6;
}

.boxes li:nth-child(4) {
  z-index: 5;
}

.boxes li:nth-child(5) {
  z-index: 4;
}

.boxes li:nth-child(6) {
  z-index: 3;
}

.boxes li:nth-child(7) {
  z-index: 2;
}

.boxes li:nth-child(8) {
  z-index: 1;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

Answer 2

不幸的是，可能没有CSS唯一的解决方案——CSS3个转换创建了一个新的堆叠上下文 - 参见相关文档描述和另一种效果：

If the property has a value different than none, a stacking context will be created.

Source: MDN

你可以很容易地用position: relative替换那里的translate(0,0)并在.template-options-dropdown中添加一个大于零的z-index来解决问题.

$(document).ready(function() {
  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parent().find('.template-options-dropdown').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  /*transform: translate(0, 0);*/
  position: relative; /*ADDED*/
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
  z-index: 2;/*ADDED*/
}

.template-options-dropdown.open {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

A hacky 解决方案搞乱了 wrapping - 您可以添加更多转换：

为 ul 添加 scaleY(-1) 使列表向后排列，因为索引较高的列表项位于索引较低的列表项之上。
给li添加一个反转scaleY(-1)，让世界恢复正常。
也清除 li浮动。

参见下面的演示：

$(document).ready(function() {
  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parent().find('.template-options-dropdown').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
  transform: scaleY(-1);/*ADDED*/
}
.boxes:after {/*ADDED*/
  content: '';
  clear: both;
  display: block;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  transform: translate(0, 0) scaleY(-1);/*ADDED*/
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
}

.template-options-dropdown.open {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

如果translate(0,0)仍然无法删除，你别无选择，只能使用javascript:

通过给定一个等于列表中索引的 z-index 来反转列表堆叠。
将position:relative添加到li

参见下面的演示：

$(document).ready(function() {

  // ADDED
  $($('ul.boxes > li').get().reverse()).each(function(index){
     $(this).css('z-index', index);
  });

  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parent().find('.template-options-dropdown').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  transform: translate(0, 0);
  position: relative;/*ADDED*/
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
}

.template-options-dropdown.open {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

Answer 3

你很接近，但如果是我，我会在 <li> 或 div.download-container 上设置 .open class，设置一个巨大的 z-使用那个索引，并使用级联打开子菜单。我们还必须在要设置 z-index 的元素上设置 position:relative;，否则 z-index 什么都不做。

示例：

$(document).ready(function() {
  $('button[name="button"]').click(function(e) {
    $(e.currentTarget).parents('li').toggleClass('open');
  });
});

.boxes {
  list-style-type: none;
}

.boxes >li {
  float: left;
  width: 100px;
  height: 100px;
  background-color: red;
  margin: 5px;
  transform: translate(0, 0);
  position:relative;
}

.boxes >li.open {
    z-index:500;
}

.download-container {
  background: rgba(40, 39, 39, 0.8);
  bottom: 0;
  position: absolute;
  text-align: center;
  width: 100%;
}

.download-container .dropdown-container {
  display: inline-block;
  position: relative;
}

.download-container .dropdown-container button {
  background: #0bb9ab;
  color: #fff;
  padding: 6px 12px;
}

.template-options-dropdown {
  list-style-type: none;
  text-align: left;
  padding: 0;
  position: absolute;
  background-color: #111;
  visibility: hidden;
}

.boxes li.open .template-options-dropdown {
  visibility: visible;
}

.template-options-dropdown li a {
  color: white;
  text-decoration: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul class="boxes">
  <li>
    <div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div>
  </li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
  <li><div class="download-container">
      <div class="dropdown-container">
        <button type="button" name="button">Download</button>

        <ul class="template-options-dropdown">
          <li>
            <a href="#">Original</a>
          </li>
          <li>
            <a href="#">Thumb</a>
          </li>
          <li>
            <a href="#">Mobile</a>
          </li>
          <li>
            <a href="#">Tab</a>
          </li>
          <li>
            <a href="#">Web</a>
          </li>
          <li>
            <a href="#">Large web</a>
          </li>
        </ul>
      </div>
    </div></li>
</ul>

具有变换的元素内的子元素 z-index 属性

Child element z-index inside element with transform property

html

css

z-index

css-transforms