JSFiddle - React, Tailwind, and code Playground

HTML

<div class="layout">
  <div class="sidebar sidebar--left">left</div>
  <div class="sidebar sidebar--right">right</div>
  <div class="content">content</div>
</div>

CSS

*,
*:before,
*:after {
  box-sizing: border-box;
}

.content {
  margin-right: 300px;
  margin-left: 300px;
}

.sidebar {
  width: 300px;
}

.sidebar--left {
  float: left;
}

.sidebar--right {
  float: right;
}

.content,
.sidebar {
  border: 1px solid #333;
  background-color: #eee;
}