JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://getbootstrap.com/dist/css/bootstrap.css">
<script src="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/2.1.0/bootstrap.min.js"></script>
<div class="navbar navbar-inverse navbar-fixed-top">

        </div>

        <div class="fixedThing"></div>

        <p>...insert lots of page content so it scrolls ...</p>

CSS

.fixedThing {
                position: fixed;
                width: 100%;
                height: 100%;
                background: red;
                opacity: 0.5;
            }

            .navbar {
                width: 100%;
            }