Here is some code which i not too long ago wrote. I believe that it offers a essential explanation of mixing course/ID names with pseudoclasses. What's the distinction between # and . when declaring a set of types for an element and what are the semantics that occur into play https://www.presta-addons-modules.com/en/front-office/prestashop-scrolling-info-based-on-selected-category-and-language.html