oroboto/base64-drag-and-drop — reverse-engineered prompt

Build me a super simple little browser tool that turns files into base64 just by dragging them onto the page.

I want it to be basically self contained in one HTML file if possible, so I can just open it locally and use it without setting up anything complicated. It should let me drag and drop any file from my computer into a clear drop area, then show me the base64 output right away so I can copy it. If the file is an image, also show a preview using a data URI because that is handy for CSS and quick testing.

A big requirement is that it works offline and does not upload files anywhere, since the whole point is keeping sensitive files local and private. Please make it work well in Firefox and Chrome, with the local file behavior handled as nicely as those browsers allow.

Keep the interface minimal and obvious. If you need to, look up current browser support details online.