JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a" class="container">
<section>a</section>
<aside>b</aside>
</div>

<div class="clearfix"></div>

<div id="b" class="container">
<section>a</section>
<aside>b</aside>
</div>

CSS

#a {
  width: 804px;
}

#a * {
  border: 1px solid red;
}

#b * {
  border: 1px solid blue;
}

#b {
  width: 600px;
}

section {
  width: 400px;
  float: left;
}

aside {
  width: 400px;
  float: right;
}

.container:before,
.container:after {
  content:"";
  display:table;
}
.container:after {
  clear:both;
}
.container {
  zoom:1; /* For IE 6/7 (trigger hasLayout) */
}