Category on Submenu

Hello guys,

As the title says, I know this is an easy task, but, I can’t seem to make this work.

Here is a sample site: CLICK

The menu there is the “about”, “works”, and “contact”, and the submenu “poem” should be under works.

My functions.php for registering menu is:

function register_my_menus() {
  register_nav_menus(
    array(
      'header-menu' => __( 'Header Menu' ),
      'extra-menu' => __( 'Extra Menu' )
    )
  );
}
add_action( 'init', 'register_my_menus' );

The header where the menu appears is:

<div id="navmenu">
   <center>
	<?php wp_nav_menu( array( 'theme_location' => 'header-menu', 'container_class' => '' ) ); ?>
   </center>
</div>

Now, it should appear like this, right? And on view-source, it appears that way, but look at the link ?? it doesn’t look good :)))

<div id="navmenu">
  <center>
     <div class="menu-header-menu-container">
         <ul id="menu-header-menu" class="menu">
               <li id="menu-item-9" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-2 current_page_item menu-item-9"><a href="https://dmdoomlord.byethost7.com/">About</a></li>
               <li id="menu-item-8" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-8"><a href="https://dmdoomlord.byethost7.com/work/">Works</a>
                     <ul class="sub-menu">
	                     <li id="menu-item-152" class="menu-item menu-item-type-taxonomy menu-item-object-category menu-item-152"><a href="https://dmdoomlord.byethost7.com/category/poem/">Poem</a></li>
                     </ul>
               </li>
               <li id="menu-item-11" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-11"><a href="https://dmdoomlord.byethost7.com/contact/">Contact</a></li>
         </ul>
      </div>
   </center>
</div>

Thanks community ??