z-index and nested DOM elements (stacked context) overlay

Question

How do I make div3 & div4 above div1 and div2 without using "ID" selector on CSS level?

.container {
    margin: 50px;
    padding: 20px;
    text-align: center;
    border: 1px dashed #999966;
}

.position {
  height: 120px;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  margin-bottom: 10px;
  opacity: 0.8;
  border: 1px dashed #999966;
  background-color: #ffffcc;
}

.position .position {
  margin-top: 60px;
  margin-left: 100px;
  width: 50%;
}

.relative {
  position: relative;
  border: 1px dashed #669966;
  background-color: #ccffcc;
 }
 
.fixed {
  position: fixed;
  border: 1px dashed #669966;
  background-color: #e3e3ff;
  align-items: flex-start;
 }
 
.fixed.target-block {
  width: 200px;
  height: 300px;
  top: 130px;
  right: 140px;
  z-index: 999;
 }
 

<div class="container">
  <p>
    DIV: CONTAINER<br>
    position: relative;
  </p>

  <div class="position">
    <p>
      DIV #1<br>
      no position;
    </p>
    <div class="position relative">
      <p>
        DIV #3<br>
        position: relative;<br>
        parent
      </p>
      <div class="position fixed target-block">
        <p>
          DIV #4<br>
          position: fixed;<br>
          child
        </p>
      </div>
    </div>
  </div>
  
  <div class="position">
    <p>
      DIV #2<br>
      no position;
    </p>
  </div>
  
</div>

Answer 1

If we refer to the specification we can read this:

8. All positioned, opacity or transform descendants, in tree order that fall into the following categories: ...

9. All opacity descendants with opacity less than 1, in tree order, create a stacking context generated atomically.

And in your case Div #2 will create it's own stacking context like Div #1 and since none of them is positioned with z-index you cannot achieve what you want by simply controling their child elements.

So the only way I see here is to make one of the divs positioned and apply z-index to it or both of them positionned with different z-index. The purpose is to avoid following the tree order like specified above.

.container {
  margin: 50px;
  padding: 20px;
  text-align: center;
  border: 1px dashed #999966;
}

.position {
  height: 120px;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  margin-bottom: 10px;
  opacity: 0.8;
  border: 1px dashed #999966;
  background-color: #ffffcc;
}

.position .position {
  margin-top: 60px;
  margin-left: 100px;
  width: 50%;
}

.relative {
  position: relative;
  border: 1px dashed #669966;
  background-color: #ccffcc;
}

.fixed {
  position: fixed;
  border: 1px dashed #669966;
  background-color: #e3e3ff;
  align-items: flex-start;
}

.fixed.target-block {
  width: 200px;
  height: 300px;
  top: 130px;
  right: 140px;
  z-index: 999;
}

<div class="container">
  <p>
    DIV: CONTAINER<br> position: relative;
  </p>

  <div class="position" style="position:relative;z-index:1;">
    <p>
      DIV #1<br> no position;
    </p>
    <div class="position relative">
      <p>
        DIV #3<br> position: relative;<br> parent
      </p>
      <div class="position fixed target-block">
        <p>
          DIV #4<br> position: fixed;<br> child
        </p>
      </div>
    </div>
  </div>

  <div class="position">
    <p>
      DIV #2<br> no position;
    </p>
  </div>

</div>

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