All you have to do is read the code on getbootstrap.com:
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>_x000D_
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css">_x000D_
_x000D_
<nav class="navbar navbar-inverse navbar-static-top" role="navigation">_x000D_
<div class="container">_x000D_
<div class="navbar-header">_x000D_
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">_x000D_
<span class="sr-only">Toggle navigation</span>_x000D_
<span class="icon-bar"></span>_x000D_
<span class="icon-bar"></span>_x000D_
<span class="icon-bar"></span>_x000D_
</button>_x000D_
</div>_x000D_
_x000D_
<!-- Collect the nav links, forms, and other content for toggling -->_x000D_
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">_x000D_
<ul class="nav navbar-nav">_x000D_
<li><a href="index.php">Home</a></li>_x000D_
<li><a href="about.php">About</a></li>_x000D_
<li><a href="#portfolio">Portfolio</a></li>_x000D_
<li><a href="#">Blog</a></li>_x000D_
<li><a href="contact.php">Contact</a></li>_x000D_
</ul>_x000D_
</div>_x000D_
</div>_x000D_
</nav>
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