JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">
<button class="full">
asdasdasd
</button>

<span class="expand">Test2</span>

</div>

CSS

.test{
  width: 100%;
  background-color: red;
}

.expand{
  display: block;
  background: green;
}

.full{
  width: 100%;
}