A theme is a universal lesson learned and the central idea is a one-sentence main idea.
1. The central idea conveys that the text is about mainly, whereas, the theme refers to the author's message, life lesson, or moral learned from the story.
2. A central idea cannot be referred to as the topic of the text, on the other hand, a theme cannot be the same as a topic.
3. In one sentence, the central idea can be stated, whereas, themes are repeated and can be multiple.
4. Therefore, a theme is not the central idea, nor it can act as a topic of the text.