For the Business Casual column, we go behind the scenes at various local workplaces to see what staffers wear to the office. At the Boston Ballet’s South End offices and studio, the team is gearing up for the debut of Mikko Nissinen’s “The Nutcracker” on Nov. 23, and we were able to see what they wear during one of their busiest times of the year. While the costume department created the nearly 350 new costumes for the production, the creative and production teams planned how to pack the theater and fill the stage. Meanwhile, the dancers rehearsed, ready to face what the season has in store, inside and outside the studio.