JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
   <style type="text/css">
      body {padding:20px;}
      #outer {background-color:#ff0000; width: 100%;}
      #inner {width:500px; background-color:#ff0000; border: solid 1px blue}   
   </style>
</head>
<body>
     <div id="outer">
        <div id="inner">
           <p>Why the hell outer div bg color does not expand?</p>
           <p>Why the hell outer div bg color does not expand?</p>
           <p>Why the hell outer div bg color does not expand?</p>
        </div>
     </div>
</body>
</html>