JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <section>Section</section>
  <aside>Aside</aside>
</div>

CSS

* {
  box-sizing: border-box;
}

.container {
  background: #eee;
  width: 100%;
  padding: 20px;
}

.container::after {
  content: "";
  display: block;
  clear: both;
}

section,
aside {
  background: #0078D7;
  color: #fff;
  padding: 20px 0;
  text-align: center;
}

section {
  float: left;
  width: 65%;
}

aside {
  float: right;
  width: 30%;
}
@media only screen and (max-width: 768px) {
  section,
  aside{
  width: 100%}
}