conditional statement with wp_list_categories

Hi,

I have a question about where to place a conditional statement with a dropdown menu and wp_list_categories. Have searched and tried many things but nothing works.

Here’s my site for reference: https://newsite.blairshapiro.com

Here’s my header.php code to create a dropdown menu:

<li>

          <a>Work</a>

                 <ul>
                     <?php wp_list_categories("exclude=$blog_ID&title_li="); ?>
    		</ul>
         </li>

I want to highlight ‘Work’ when in one of the subcategories created by wp_list_categories and think I need to place the following conditional statement in either the “li” segment or the “ul” segment:

<?php if(is_category){ echo ' class="current_page_item" ';}?>>

My question is, where do i place the conditional statement and how to best style the css so ‘Work’ is highlighted when in one of the subcategories created by wp_list_categories?

Any help would be appreciated!