Yes, the dress code rules are public but they are not well documented
Jen*, a staffer working for a Democratic senator: Every individual senate office is like its own small business. The tone when it comes to vacation policy and office hierarchy and dress code is set by every office independently. I have the benefit of working for someone who is really pragmatic about dressing and would prefer that people are in comfortable shoes as opposed to stylish shoes. I think there are other offices that put more of a premium on presentation, so their dress codes are stricter.
That said, Congress is an institution, and it’s an arcane institution. There are rules about what you can and can’t wear on the senate floor. Men have to be in suit and tie. For women, if you’re wearing a dress, you have to have your shoulders covered. If you’re wearing slacks, you have to wear a jacket. One day I was in slacks and a sweater and I tried to swipe onto the floor and the sergeant at arms said, “You can’t be out there, you don’t have a jacket on.” My boss was with me and was like, “Really?” They were like, “Unfortunately, she can’t accompany you.”