JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">
    HEADER
</div>
<div id="content">
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
    CONTENT<br />
</div>

CSS

body {
    font-family: Arial,Helvetica,sans-serif;
    color: #fff;
    font-size: 12px;
}
#header {
    top: 0;
    width: 0;
    right: 0;
    position: fixed;
    height: 50px;
    line-height: 50px;
    z-index: 999;
    background: #333;
    text-align: center;    
}
#content {
    margin-top: 50px;
    position: relative;
    background: #666;
    text-align: center;
    height: 1000px;
}