JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="inner-item"></div>
  <div class="width-item"></div>
</div>

CSS

div {
  display: inline-block;
}

.container {
  background-color: yellow;
}

.width-item {
  width: 100px;
  height: 100px;
  background-color: red;
}

.inner-item {
  width: 100%;
  height: 100px;
}