JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="first">
    first
  </div>
  <div class="second">
    <div class="second-inner">
      second
    </div>
  </div>
</div>

CSS

.first, .second, .second-inner {
  height: 50px;
  width: 50px;
}

.first {
  background-color: wheat;
  
}

.second {
  display: flex;
  flex-direction: column;
  justify-content: center;
  height: 100%;
}

.second-inner {
  background-color: purple;
}

.container {
  background-color: silver;
  height: 400px;
  display: flex;
  flex-direction: column;
}