Lower z-indexed parent's child upon higher z-indexed element?

Question

Is there a way to manipulate the stacking context this way? I want the text to be on the top of the blue element.

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Answer 1

It is unfortunately impossible to break the stacking context in this way, as a child's z-index is set to the same stacking index as its parent. You will need to make the text a sibling element, and additionally make sure it has a position other than static in order for the z-index to apply.

From here, it's a simple matter of positioning it as desired (in this case with top: 150px and left: 150px.

This can be seen in the following:

div {
  width: 200px;
  height: 200px;
  position: absolute;
}

#a {
  z-index: 0;
  background-color: red;
  left: 150px;
  top: 150px;
}

#b {
  z-index: 1;
  background-color: blue;
  left: 0;
  top: 0;
}

p {
  position: absolute;
  z-index: 2;
  top: 150px;
  left: 150px;
}

<div id="a"></div>
<div id="b"></div>
<p>verylongtext</p>

Answer 2

Yes you can, the trick is to keep the red element with z-index:auto so that p will not belong to its stacking context and can be placed above the blue element.

auto

The box does not establish a new local stacking context. The stack level of the generated box in the current stacking context is the same as its parent's box.^ref

Don't forget to make the p positioned in order to be able to use z-index:

div {
  width: 200px;
  height: 200px;
  position: absolute;
}

#a {
  background-color: red;
  left: 150px;
  top: 150px;
}

#b {
  z-index: 1;
  background-color: blue;
  left: 0;
  top: 0;
}

p {
  z-index: 2;
  position: relative;
}

<div id="a">
  <p>verylongtext</p>
</div>
<div id="b"></div>

You can also remove everything and play only with margin:

div {
  width: 200px;
  height: 200px;
}

#a {
  background-color: red;
  margin-left: 150px;
  margin-top: 150px;
  overflow:hidden; /*remove margin-collapsing*/
}

#b {
  background-color: blue;
  margin-top: -350px;
}

<div id="a">
  <p>verylongtext</p>
</div>
<div id="b"></div>

You can refer to this question ( Strange behavior of background when elements are overlapping) to understand how it works.