What is the main idea of Huckleberry Finn?

Can you sum up the central theme of Huckleberry Finn in a concise manner? What is the message that Mark Twain is trying to convey through the story and the characters? Is it about the struggles of a young boy growing up, the complexities of morality and social norms, or something else entirely? And how does the novel's portrayal of slavery and racial inequality factor into its main idea?