"The big shirt."
Translation:Το μεγάλο πουκάμισο.
It's true that the Clothing vocabulary translation has been giving some trouble to all Duolingo courses. For my target languages, I personally like using Google Images in such cases - it makes learning a word much easier. In our case here, Google returns results for button-up and button-down shirts as well.
Yes, all the image search results for πουκάμισο fall under the category of what I'd call a shirt in English. But then in my variety of English, "button-down shirt" is a subclass of shirts, not a category that's separate from shirts.
The things called μπλούζα would be "sweatshirt" or "long-sleeved T-shirt" or just "top" to me.