sarthakvs/youtube_to_mp3_converter ? reverse-engineered prompt

Build me a simple web app where someone can paste a YouTube link, hit Convert, and then download the audio as an MP3 file.

It should feel easy and straightforward, with one main page, a clean input box, a Convert button, and a clear download link or button when the file is ready. If the link is missing or invalid, show a friendly error message instead of breaking. Make it look decent on desktop and mobile, and keep the flow as simple as possible so a normal person can use it without thinking.

If you need to look up current docs online for anything, go ahead. I just want a working YouTube to MP3 converter website that matches that basic experience.