Bootstrap navbar is displaying vertically instead of horizontally - html

Question

I'm working on a project using CodePen and I'm using bootstrap to make a navbar. But for some reason it's displaying vertically instead of horizontally. Even when I copy and paste code from the W3Schools examples and the Bootstrap website. I don't know what else to do. Please help.
This is the W3Schools example code:
<nav class="navbar navbar-default">
<div class="container-fluid">
<div class="navbar-header">
<a class="navbar-brand" href="#">WebSiteName</a>
</div>
<ul class="nav navbar-nav">
<li class="active">Home</li>
<li>Page 1</li>
<li>Page 2</li>
<li>Page 3</li>
</ul>
</div>
This is example code from the Bootstrap website:
<nav class="navbar navbar-default">
<div class="container-fluid">
<!-- Brand and toggle get grouped for better mobile display -->
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#">Brand</a>
</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 class="active">Link <span class="sr-only">(current)</span></li>
<li>Link</li>
<li class="dropdown">
Dropdown <span class="caret"></span>
<ul class="dropdown-menu">
<li>Action</li>
<li>Another action</li>
<li>Something else here</li>
<li role="separator" class="divider"></li>
<li>Separated link</li>
<li role="separator" class="divider"></li>
<li>One more separated link</li>
</ul>
</li>
</ul>
<form class="navbar-form navbar-left">
<div class="form-group">
<input type="text" class="form-control" placeholder="Search">
</div>
<button type="submit" class="btn btn-default">Submit</button>
</form>
<ul class="nav navbar-nav navbar-right">
<li>Link</li>
<li class="dropdown">
Dropdown <span class="caret"></span>
<ul class="dropdown-menu">
<li>Action</li>
<li>Another action</li>
<li>Something else here</li>
<li role="separator" class="divider"></li>
<li>Separated link</li>
</ul>
</li>
</ul>
</div><!-- /.navbar-collapse -->
Both do not work. And yes, I've triple checked my <link> and <script> tags.
Edit: here is my CodePen

Answer 1

First like in the comments you are using bootstrap 3 markup and you are linking to both bootstrap 3 and 4 remove the bootstrap 4 css. Then you need to have the div with the class of collapse navbar-collapse so just add this to the div that has the id of nav just like the following:
<nav class="navbar navbar-inverse">
<div class="container-fluid">
<div class="navbar-header">
<a class="navbar-brand" href="#about">
<span style="font-family: 'Source Code Pro', Monospace; color:green"><i class="fa fa-code"></i>Ryan</span></a>
</div>
<div class="collapse navbar-collapse" id="nav">
<ul class="nav navbar-nav">
<li>About</li>
<li>Portfolio</li>
<li>Contact</li>
</ul>
</div>
</div>
</nav>
You may want to add the collapse button to the navbar header as well otherwise your links wont show up at mobile widths so it would look like:
<nav class="navbar navbar-inverse">
<div class="container-fluid">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#nav" aria-expanded="false">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#about">
<span style="font-family: 'Source Code Pro', Monospace; color:green"><i class="fa fa-code"></i>Ryan</span>
</a>
</div>
<div class="collapse navbar-collapse" id="nav">
<ul class="nav navbar-nav">
<li>About</li>
<li>Portfolio</li>
<li>Contact</li>
</ul>
</div>
</div>
</nav>

Answer 2

As someone said - remove bootstrap 4 from loaded CSS files and it will work