JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.container {
  display: flex;
}

.container > div {
  display: block;
  padding: 1em 0;
  flex: 1;
  background-color: red;
}

@media (max-width: 800px) {
  .first {
    order: 2;
  }
}