What is the theme and style for Bud, not Buddy?
You have asked two questions that must be posted separately. Let me discuss the theme of the story.
Your question is about Bud, Not Buddy, written by Christopher Paul Curtis. This book is about a boy who is orphaned during the Great Depression which took place during the late 1920s and the 1930s. The reader learns about the conditions of the Depression, about Hooverville (little "cities" made up of cardboard and wood outside of main towns where people tried to survive when they had lost everything to an extremely bad economy), that during the Depression work and money were hard to come by, and so, too, were food and clothing—even having a home.
Bud is ten years old and has lost his mother in recent years. His father has never been around, and Bud learns some of life's really hard lessons not only in being moved around between foster homes, but seeing how hard it is for adults to survive as well as kids during such difficult times in the United States.
Bud is trying to find his way to the man he believes to be his father, and he must travel from Flint, Michigan, to another town, Grand Rapids, which could easily take two days to reach on foot. With some help along the way, Bud finally reaches Herbert Calloway, and there is a secret Mr. Calloway holds as to who Bud really is.
There are several themes in the story: some may be different for different people based on the message each reader picks up from the author.
One theme is that family is very important, and that sometimes it is stronger than almost every other problem someone could think of.
Another theme is that life is hard, and sometimes you have to stand up for what you believe and be brave, even when you're afraid.
A third theme may be that if you want something very badly, and work really hard, you may not get exactly what you were hoping for, but the hard work will eventually pay off.
After reading this book, I believe you will be able to see how each of these themes is present in the novel.