The Claude prompt

Create an interactive prototype as a SINGLE, self-contained index.html file.

Hard requirements:
- One file only. Put ALL CSS in a <style> tag and ALL JavaScript in a <script> tag inside that same index.html. No separate .css or .js files.
- No build step and no server: it must work when the file is opened directly in a browser (double-click).
- External libraries are allowed ONLY from https://cdnjs.cloudflare.com. Do not depend on any other external host, API, or backend.
- Embed any images or fonts inline as data: URLs (or draw them in code). Do not link to local files.
- Use only in-memory state. Do NOT use localStorage, sessionStorage, cookies, or IndexedDB.
- Make it responsive so it looks right on a laptop and inside an embedded panel.
- Give it a clear title and a polished, self-explanatory UI.

When you're done, output the complete index.html as a single downloadable file named index.html.

What I want to prototype: [describe your idea here]