Dining room is more formal than the bar lounge area. Dining crowd is usually business casual. But you won't feel out of place in Jean's with a dress shirt.
I went with a group of coworkers, most of us wearing jeans and button down shirts and we were not seen as under dressed.
We dressed up the first time we went to weeknight evening dinner (dress for me, dress pants and dress shirt for hubby) and felt a little over dressed... Nice jeans, nice shoes, nice shirt would fit well.
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