JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div class="inside-1">
        <h3>This is the left area</h3>
    </div>
    <div class="inside-2">
        <h3>This is the right area</h3>
    </div>
</div>

CSS

* {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box; }

.wrapper {
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
  border: 1px solid #0f0;
  padding: 40px 10%; }

.wrapper:after {
    content: '';
    display: table;
    clear: both;
}

.inside-1 {
  display: block;
  float: left;
  margin-right: 5%;
  border: 1px solid #f00;
  width: 65%; }

.inside-2 {
  display: block;
  float: left;
  margin-right: 0;
  border: 1px solid #00f;
  width: 30%; }