The upstairs is formal and downstairs more casual but nothing is required, I'm not sure you would be able to dine in shorts and a T shirt though
Ive seen folks wear sweatshirts upstairs before but they were definitely underdressed. I'd recommend thr tavern below if you're looking for a more casual vibe.
I beleive there is no offical dress code. Formal is the most common attire. I would recommend nothing less than business casual.
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