JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<nav id="main-menu">
	<div class="container">
		<ul class="nav">
			<li id="item1"><a href="#">Menu item 1</a></li>
			<li id="item2"><a href="#">Menu item 2</a></li>
			<li id="item3"><a href="#">Menu item 3</a></li>
			<li id="item4"><a href="#">Menu item 4</a></li>
			<li id="item5"><a href="#">Menu item 5</a></li>
		</ul>
	</div>
</nav>

<div id="content">
	<div class="container">
		<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce bibendum odio et interdum pretium. Vivamus in scelerisque diam. Etiam sem tortor, faucibus in sollicitudin et, ultrices non ex. Pellentesque at nisi mattis, pellentesque elit eget, viverra orci. Mauris volutpat augue tortor, eget consequat velit venenatis ac. Cras at dolor eu eros bibendum fermentum quis ac mi. Donec sodales sed turpis eu commodo. Vestibulum arcu neque, euismod at blandit sed, aliquet sed odio. Curabitur porttitor posuere massa, ut pellentesque diam vehicula sagittis.</p>
		<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce bibendum odio et interdum pretium. Vivamus in scelerisque diam. Etiam sem tortor, faucibus in sollicitudin et, ultrices non ex. Pellentesque at nisi mattis, pellentesque elit eget, viverra orci. Mauris volutpat augue tortor, eget consequat velit venenatis ac. Cras at dolor eu eros bibendum fermentum quis ac mi. Donec sodales sed turpis eu commodo. Vestibulum arcu neque, euismod at blandit sed, aliquet sed odio. Curabitur porttitor posuere massa, ut pellentesque diam vehicula sagittis.</p>
		<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce bibendum odio et interdum pretium. Vivamus in scelerisque diam. Etiam sem tortor, faucibus in sollicitudin et, ultrices non ex. Pellentesque at nisi mattis, pellentesque elit eget, viverra orci. Mauris volutpat augue tortor, eget consequat velit venenatis ac. Cras at dolor eu eros bibendum fermentum quis ac mi....

CSS

body {
  background-color: #000;
  color: #fff;
  font-size: 17px;
  min-width: 1170px;
}
.container {
  width: 1170px;
}
#main-menu {
  position: absolute;
  height: 68px;
  width: 100%;
  display: block;
  top: 0px;
  z-index: 500;
  background-color: rgba(0, 0, 0, 0.8);
  border-bottom: 2px solid #fff;
  text-transform: uppercase;
}
#main-menu li {
  display: block;
  float: left;
  position: relative;
  font-size: 24px;
  font-weight: 700;
  height: 68px;
  line-height: 25px;
  padding: 20px 18px;
}
#main-menu li a {
  padding: 0;
  color: #999;
  text-shadow: none;
}

JavaScript

var alignMenu = function() {
    $('#main-menu').css({
        'top': $('body').scrollTop(),
        'width': $('#content').width()
    })
}

$(window).scroll(function(){ alignMenu() });
$(window).resize(function(){ alignMenu() });