CSS：使元素的 z-index 低于兄弟姐妹的 child

Question

问题是 header：我需要它看起来固定在固定部分并且仍然可以点击。当第一部分滚动到 header 时，它应该覆盖 header.

我可以随意移动或更改 header：

<a href="#" class="header">
  THIS IS THE HEADER 
  <span style="font-size: 12px;">(you can hover me)</span><br>
  <span style="font-size: 14px; font-style: italic; letter-spacing: 0.05em;">which should be <br> OVER "invisible section" AND "fixed section" <br> BUT UNDER "first section", <br>WHILE maintaining fixed position</span>
</a>

虽然我可以将 header 添加到不可见部分，但我无法更改部分的整体结构：

<div class="section section-fixed">
  fixed section underneath "invisible section"
</div>
<div class="wrapper">
  <div class="section section-invisible">
    <h2>invisible section</h2>
  </div>
  <div class="section section-first">
    first section
  </div>
</div>

我尝试将 header 添加到不可见部分，虽然这有助于保持 header 可点击，但我无法使其看起来与固定部分一样固定。

我意识到描述它可能会造成混淆，所以这里有一些附带的图片，请查看 FIDDLE

@import url("https://fonts.googleapis.com/css2?family=Baloo+Da+2&display=swap");
html {
  box-sizing: border-box;
}

*, *:before, *:after {
  box-sizing: inherit;
}

html, body {
  margin: 0;
  padding: 0;
}

body {
  font-size: 16px;
  font-family: 'Baloo Da 2', cursive;
}

.header {
  background: floralwhite;
  display: inline-block;
  padding: 10px;
  position: fixed;
  z-index: 3;
  left: 30px;
  top: 30px;
  color: inherit;
  text-decoration: none;
  line-height: 1.2;
  box-shadow: 0 0 0 rgba(0, 0, 0, 0.5);
  transition: all .5s ease;
}
.header:hover {
  box-shadow: 2px 3px 10px rgba(0, 0, 0, 0.5);
  background-color: pink;
}

.wrapper {
  border: 2px solid red;
  z-index: 2;
  position: relative;
}

.section {
  padding: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
}
.section-fixed {
  background: gray;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1;
}
.section-invisible {
  align-items: flex-end;
  padding: 0;
}
.section-invisible h2 {
  background: goldenrod;
  padding: 50px;
  margin: 0;
  width: 100%;
  text-align: center;
}
.section-first {
  background: darkslateblue;
  color: white;
}

<a href="#" class="header">
  THIS IS THE HEADER 
  <span style="font-size: 12px;">(you can hover me)</span><br>
  <span style="font-size: 14px; font-style: italic; letter-spacing: 0.05em;">which should be <br> OVER "invisible section" AND "fixed section" <br> BUT UNDER "first section", <br>WHILE maintaining fixed position</span>
</a>
<div class="section section-fixed">
  fixed section underneath "invisible section"
</div>
<div class="wrapper">
  <div class="section section-invisible">
    <h2>invisible section</h2>
  </div>
  <div class="section section-first">
    first section
  </div>
</div>

初始：

滚动后：

Answer 1

更新您的 z-index，如下所示。最重要的是不要将任何 z-index 设置为 wrapper:

@import url("https://fonts.googleapis.com/css2?family=Baloo+Da+2&display=swap");
html {
  box-sizing: border-box;
}

*,
*:before,
*:after {
  box-sizing: inherit;
}

html,
body {
  margin: 0;
  padding: 0;
}

body {
  font-size: 16px;
  font-family: 'Baloo Da 2', cursive;
}

.header {
  background: floralwhite;
  padding: 10px;
  position: fixed; 
  z-index: 2; /* here */
  left: 30px;
  top: 30px;
  color: inherit;
  text-decoration: none;
  line-height: 1.2;
  box-shadow: 0 0 0 rgba(0, 0, 0, 0.5);
  transition: all .5s ease;
}

.header:hover {
  box-shadow: 2px 3px 10px rgba(0, 0, 0, 0.5);
  background-color: pink;
}

.wrapper {
  border: 2px solid red;
  position: relative;
}

.section {
  padding: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
}

.section-fixed {
  background: gray;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1; /* here */
}

.section-invisible {
  align-items: flex-end;
  padding: 0;
  position: relative;
  z-index: 1; /* here */
}

.section-invisible h2 {
  background: goldenrod;
  padding: 50px;
  margin: 0;
  width: 100%;
  text-align: center;
}

.section-first {
  background: darkslateblue;
  color: white;
  position: relative;
  z-index: 2; /* here */
}

<a href="#" class="header">
  THIS IS THE HEADER 
  <span style="font-size: 12px;">(you can hover me)</span><br>
  <span style="font-size: 14px; font-style: italic; letter-spacing: 0.05em;">which should be <br> OVER "invisible section" AND "fixed section" <br> BUT UNDER "first section", <br>WHILE maintaining fixed position</span>
</a>
<div class="section section-fixed">
  fixed section underneath "invisible section"
</div>
<div class="wrapper">
  <div class="section section-invisible">
    <h2>invisible section</h2>
  </div>
  <div class="section section-first">
    first section
  </div>
</div>

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