The code has class names col-4 and col-8 where as the instructions mention class names as col-md-4 and col-md-8.
<main>
<div class="container">
<div class="row">
<div class="col-4">
<div class="card">
<div class="card-body">
<h3>Menu</h3>
<p>This is the left side of my web page. It occupies 33% of the total width</p>
</div>
</div>
</div>
<div class="col-8">
<div class="card">
<div class="card-body">
<h2 class="text-center">Main content</h2>
<p>Here it goes the main content of my web page.</p>
</div>
</div>
</div>
</div>
</div>
</main>
In our case, we created just 2 columns , but we defined the first one with [4] units (col-md-4 ) and the second with [8] units (col-md-8 ).