JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Site</title>
<link href="style.css" rel="stylesheet" type="text/css" />
</head>

<body style="background: #933;padding:0;margin:0;height:100%;">
 <div class="header">
  <div class="headeron">
  </div>
 </div>
</body>
</html>

CSS

@charset "utf-8";
/* CSS Document */

.header {
    background: #000;
    width:1100px;
    height:150px;
    margin:auto;
    border:0px solid #000;
    -webkit-border-bottom-right-radius: 10px;
    -webkit-border-bottom-left-radius: 10px;
    -moz-border-radius-bottomright: 10px;
    -moz-border-radius-bottomleft: 10px;
    border-bottom-right-radius: 10px;
    border-bottom-left-radius: 10px;
    z-index:2;
}

.headeron {
    border:0px solid #000;
    margin-top:10px;
    padding-left:10px;
    padding-right:10px;
    background-color:#FFF;
    width:1080;
    height:100px;
    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    border-radius: 10px;
    z-index:5000;
}