Current menu item to stay highlight when on blog post

Hi there, I’ve been playing about for a couple of hours now but after trying everything I know I just can’t get this to work.

I’m trying to ensure that any ‘article’ page highlights the article top menu item. It works for this: https://www.richlywills.com/article/
but not for any single post page like this https://www.richlywills.com/article/why-innovation-is-important/

Any help would be appreciated. Thanks.