JSFiddle - React, Tailwind, and code Playground

HTML

<div class='list'>
  <div class='parent'>
    <div class='child'> Hello </div>
  </div>
  <div class='parent'>
  </div>
  <div class='parent'>
  </div>
  <div class='parent'>
  </div>
</div>

CSS

.list {
    display: flex;
    flex-direction: column;
    height: 256px;
}
.parent {
    height: 100%;
    width: 128px;
    margin-bottom: 3px;
    flex: 1 1 0%;
    overflow-y: visible;
    display: flex;
    flex-direction: row;
    background: blue;
}

.child {
    height: 48px;
    background: red;
    z-index: 2;
}

.child:hover {
    height: 128px;
}