How to make clicking a category display all its items under the category name??

[gjh42]

The $div_class='category-subs-selected'; lines in the file I mentioned create the classname. You would need to add $div_class to the output in the bottom of the file, perhaps like

    //add content
     
    $content .= $indent.$separator.'<a class="'. $a_class . ' ' . $div_class .'" href="'. $link .'">'. $box_categories_array[$i]['name'] .'</a>'. $count .
    '<br />'; 

It looks like the $div_class code is not smart enough to catch all of the active tree, so that may need modifying.
Once that appears correctly, you can style the links based on class tags like .category-top, .category-subs-selected, etc. and hide the ones you don't want to see.