Excuse me, are you standing or sitting when you go to the American embassy for an interview? Relax inside? thank you

There are many people inside, usually staying in it for about 2-3 hours. The temperature is average. But you should wear warm clothes when it is cold. The weather in Beijing is not very warm. You said about your clothes, I don't think it's very important. You pay too much attention to your clothes, and sometimes it backfires. Just be casual and tidy. As long as you can calmly answer the visa officer's questions and answer them properly. Visa is estimated to be no problem! Good luck!