JSFiddle - React, Tailwind, and code Playground

HTML

<div class="foo">
  <div class="bar">bar content</div>
  <div class="baz"></div>
</div>

CSS

.foo {
  height: 200px;
  background-color: #ccc;
}

.bar {
  background-color: GoldenRod;
}

.baz {
  background-color: Aquamarine;
}

.bar,
.baz {
  width: 100%;
}