How to add hamburger menu in bootstrap

I need some help with bootstrap nav. I want it to be toggled via a hamburger icon on mobile.

Here it is on codepen: http://codepen.io/sadman/pen/hfGwv</s> (link invalid)

.navbar,
.navbar-inverse {
  border-radius: 0;
  border: none;
  margin-bottom: 0;
  min-height: 80px;
}

.nav li {
  display: inline;
  color: white;
}

.navbar-inverse .navbar-nav>li>a {
  color: #ffffff;
  font-family: Lato;
  font-size: 1.7em;
  font-weight: 300;
  padding: 30px 25px 33px 25px;
}

.navbar-inverse .navbar-nav li a:hover {
  background-color: #444444;
  transition: 0.7s all linear;
  height: 100%;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>

All you have to do is read the code on getbootstrap.com:

Codepen

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css">

<nav class="navbar navbar-inverse navbar-static-top" role="navigation">
  <div class="container">
    <div class="navbar-header">
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
                    <span class="sr-only">Toggle navigation</span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                </button>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
        <li><a href="index.php">Home</a></li>
        <li><a href="about.php">About</a></li>
        <li><a href="#portfolio">Portfolio</a></li>
        <li><a href="#">Blog</a></li>
        <li><a href="contact.php">Contact</a></li>
      </ul>
    </div>
  </div>
</nav>

To create icon you can use Glyphicon in Bootstrap:

<a href="#" class="btn btn-info btn-sm">
    <span class="glyphicon glyphicon-menu-hamburger"></span>
</a>

And then control size of icon in css:

.glyphicon-menu-hamburger {
  font-size: npx;
}

CSS only (no icon sets) Codepen

.nav-link #navBars { margin-top: -3px; padding: 8px 15px 3px; border: 1px solid rgba(0,0,0,.125); border-radius: .25rem; }

.nav-link #navBars input { display: none; }

.nav-link #navBars span { position: relative; z-index: 1; display: block; margin-bottom: 6px; width: 24px; height: 2px; background-color: rgba(125, 125, 126, 1); border-radius: .25rem; }

<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" rel="stylesheet"/>
<nav class="navbar navbar-expand-lg navbar-light bg-light">
   <!-- <a class="navbar-brand" href="#">
      <img src="https://getbootstrap.com/docs/4.0/assets/brand/bootstrap-solid.svg" width="30" height="30" class="d-inline-block align-top" alt="">
      Bootstrap
      </a> -->
   <!-- https://stackoverflow.com/questions/26317679 -->
   <a class="nav-link" href="#">
      <div id="navBars">
         <input type="checkbox" /><span></span>
         <span></span>
         <span></span>
      </div>
   </a>
   <!-- /26317679 -->
   <div class="collapse navbar-collapse" id="navbarNav">
      <ul class="navbar-nav">
         <li class="nav-item active"><a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a></li>
         <li class="nav-item"><a class="nav-link" href="#">Features</a></li>
         <li class="nav-item"><a class="nav-link" href="#">Pricing</a></li>
         <li class="nav-item"><a class="nav-link disabled" href="#">Disabled</a></li>
      </ul>
   </div>
</nav>