XigeTime/FontAwesome-Selector — reverse-engineered prompt

Build me a small vanilla JavaScript widget for picking Font Awesome icons, like a simple icon selector I can drop into any normal HTML page.

I want it to work without jQuery or a build step. A user should be able to click a text link, span, or div, open an icon picker, browse Font Awesome icons, choose one, and have that choice applied back to the clicked element. Include the CSS and JS files needed, plus a demo page that shows how to install it and use it.

Please make it easy to add with a stylesheet in the head and a script before the closing body tag. Support a simple theme option through a data attribute, including a modern theme. Keep the code cross browser friendly for current Chrome, Firefox, Edge, Safari, Opera, and ideally older IE if practical.

Add clear README instructions, mention that Font Awesome itself must already be loaded, and include a warning that this is not production stable yet.