No matter how you cut it, The Hunger Games: Catching Fire is about ruling classes and the people they oppress. The Capitol controls the Districts, and a sacrifice is exacted through the Games.
Now that we've said that out loud, it's a movie, and movies have to depict stuff. So how do you unpack the intricacies of class struggle in 90 minutes, and have it look cool in the process? Historical references, of course, and that's what Hunger Games style is all about. So let's break it down for you.
The Capitol: The cropped jackets, high waistlines and gigantic collars refer to a style subculture in the last decades of 18th century in France, the Incroyables and Merveilleuses. These decadent youngsters epitomized extravagance. They were 18th century party animals. The Bouffants, Pomadours, and pouty lips are from the court of Ms. Let Them Eat Cake, Marie Antoinette.
The Districts: When fashionistas say workwear, they mean denim, work shirts, layers, and high boots with laces, leather aprons and riveted pockets. Workwear is just what sounds like: clothes for workers. Think Walker Evans' Dust Bowl photographs, and Steinbeck's The Grapes of Wrath. Now smear a little soot on your face, and you're good to go.