Highlight a specific page item – wp_list_pages()

Which one? If you want to highlight the Page on which you are… you need to do some more reading ??
https://codex.www.ads-software.com/Template_Tags/wp_list_pages#Markup_and_styling_of_page_items

No, not the current_page_item, another one (for example a page with page_order=9)

Right. I’m trying to figure something similar out. I’d like to start by adding a number to every <li class=” ..”> so that I can alternate colors by row, but I think that is roughly the first step for your puzzle too. To distinguish each list item with a unique class.