WordPress doesn't recognize submenus as <ul> so I can't style them properly

Question

I'm quite new to WP theme development so I'm sorry if the answer for this question may seem obvious.

I'm developing a custom WordPress theme from scratch, and I'm stuck working on the menus. My header menu has some submenus that I'd like to style, but when I call the menu with the wp_nav_menu() function, the HTML output doesn't recognize them as submenus.

I mean, even if I built correctly the menus in the admin panel, the output I get is:

<ul>
    <li>Item #1</li>
    <li>Item #2</li>
    <li>Item #3</li>
    <li>Item #4</li>
    <li>Item #5</li>
    <li>Item #6</li>
</ul>

Item #4 and Item #5 are nested into a submenu under Item #3, for example, and I want them to be nested inside another ul, how they should be. I'm sure it's a theme related problem, because everything works well by switching to a default theme.

This is how I use the wp_nav_menu() function:

wp_nav_menu( array( 'theme_location' => 'header-menu',
                    'container_class' => 'navigator' ) )

Maybe I have to add something in functions.php, but I really don't know what.

Thank you all.

Answer 1

In your array, have you tried setting depth to 0 or 2?

wp_nav_menu( array( 'theme_location' => 'header-menu',
                'container_class' => 'navigator',
                'depth' => 2) )

Where 0 should be the default and allow unlimited submenu, and 2 would allow one submenu. I am not sure how this would happen, but if it works, perhaps somewhere the default setting for depth was set to 1.

Answer 2

Apparently it was a menu registration issue. That menu was readable by WordPress, but not completely, because there were no positions available. I registered again the menu into my functions.php file and it worked. Thank you all anyway.