My book is in Chinese — the interior design looks wrong for a Chinese book. What do I do?

Use the Ming design. Open your book, find the "Book design" card on the right, and select "Ming". It is built for Chinese and other CJK books: Song/Ming (宋体) typefaces for the body text, a clean heiti (黑体) for headings, wider line spacing, and the traditional full two-character indent at the start of each paragraph. It applies to all your exports — PDF, EPUB, HTML and DOCX. If you want different choices (for example a 楷体 body), pick the "Custom" design instead and select a Chinese typeface for the paragraphs — the two-character indent is applied automatically with any Chinese body font.