I've been following a YouTube tutorial on How to create a WP theme. I don't understand how the naming of div class works in this case.

```
    <div id="container">
        <header>
            <div class="five columns clearfix">
                <a href="<?php echo get_option('home'); ?>"><img src="<?php bloginfo('template_url'); ?>/img/templogo.png" title="<?php bloginfo('title'); ?>"></a>
            </div><!--#five columns clearfix-->

            <div class="sixteen columns nav-bar">
                <?php wp_nav_menu( array('container_class' => 'main-nav', 'container' => 'nav')); ?>
            </div><!--#sixteen columns nav-bar-->                   
        </header>
    </div><!--#container-->

```

I can only guess that the "n columns" before the real nav class was for the skeleton.css we used. So to continue to my question, when we started doing CSS, we edited the "sixteen columns nav-bar" in the CSS as ".nav-bar" only, why is that? I was expecting we'll use ".sixteen columns nav-bar" since it was the div class.

Once again, I would appreciate any help and some explanation. Thank's in advance Community!