What this code does is to check if there's a child element under the dropdown with current state ('.w--current' class added by webflow), and apply the same class to the parent dropdown element.
We start by adding this short code to the Project's custom code section, so this will work globally on any page in the project.. We can also add this manually to every page we have a sub level dropdown menu.
<script>
$('.w-dropdown').each(function() {
var hasActiveLink = $(this).find('.w--current').length > 0;
$(this).find('.w-dropdown-toggle').addBack().toggleClass('w--current', hasActiveLink);
});
</script>
Based on Samuel Liew code from here.
Whenever possible, use Class Names to target the elements in your interaction. You never know when you'll need to duplicate and use it somewhere else...