JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<div id="top">
  <div id="content1">content1</div>
</div>

<div id="main">
  <div id="content2">content2</div>
</div>
</body>

CSS

#top{
  background-color : #aa5555;
  padding:10px;
  border:1px solid;
}

    html,
body{height:100%;padding:0;margin:0;border:0;}

#main{
  background-color : #5555AA;
  height:100%;
  padding:10px;
  border:1px solid;
}

#content1{
  background-color:yellow;
}

#content2{
  background-color:yellow;
  height :100%;
}