css z-index issue with nested elements

Question

I have 3 HTML elements that I want to order on the z plane:

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Answer 1

You can do this by adding z-index only to card class and placing the elements in absolute.

.bank {
  width: 150px;
  background: red;
  height: 150px;
  position: absolute;
  top: 0;
  left: 0;
}

.card {
  width: 50px;
  background: black;
  height: 50px;
  position: absolute;
  top: 0;
  left: 0;
  z-index: 1;
}

.button {
  width: 100px;
  background: blue;
  height: 100px;
  position: absolute;
  top: 0;
  left: 0;
}

<div class="bank">
   <div class="card"></div>
</div>

<div class="button"></div>

Answer 2

Don't specify any z-index to .bank to avoid creating new stacking context and simply adjust the z-index of the other elements. This will work because all the 3 elements belong to the same stacking context so you can specify any order you want.

.bank {
  position:relative;
  background: red;
  width: 500px;
  height: 200px;
}

.card {
  position: absolute;
  top:0;
  z-index: 2;
  height: 100px;
  width: 400px;
  background: blue;
}

.button {
  position: absolute;
  top: 0;
  z-index: 1;
  height: 150px;
  width: 450px;
  background: yellow;
}

.container {
  position: relative;
}

<div class="container">
  <div class="bank">
    <div class="card"></div>
  </div>

  <div class="button"></div>
</div>

UPDATE

Considering you code, the only way is to remove the z-index and transform from .bank or it will be impossible because your elements will never belong to the same stacking context. As you can read in the previous link:

Each stacking context is self-contained: after the element's contents are stacked, the whole element is considered in the stacking order of the parent stacking context.

Related for more details: Why can't an element with a z-index value cover its child?