Bootstrap columns won't go horizontal

1

So I recently began the personal portfolio project and quickly hit a brick wall. I’ve googled for answers and nothing has fixed it. No matter what I try, including all the device size codes, the columns on my screen just stay verticle no matter how much i min-max my browser. Here’s my code…

<div class="container-fluid">
  <header>
    <div class="row">
      <div class="col-xs-3">Left element</div>
      <div class="col-xs">Right element</div>
    </div>
  </header>
  <body>
  </body>
</div>

and this is how it looks…

Left element
Right element

2

Okay worked out how to show the code here.

I’d like to add that I’ve linked the CodePen project to Bootstrap 4.

3

I’ve somehow fixed it. For some reason my project hadn’t loaded bootrap 4.