JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div id="parent" (purple background div)>
    <div class="row">
      <div id="child-left" class="pull-left" (red background div)></div>
      <div id="child-right" class="pull-right" (blue background div)></div>
     </div>
    <div>
 <div>

CSS

.container {
  background-color: green;
  height:500px;
}

.container #parent {
  height:100%;
}

.container #parent .row {
  background-color: red;
  height:100%;
  position: relative;
}

.container #parent .row #child-left {
  height: 100%;
  width:30%;
  background-color: blue;
  float:left;
}

.container #parent .row #child-right {
  height: 100%;
  width:70%;
  background-color: yellow;
  float: right;
  
}