jlmakes/scrollreveal ? reverse-engineered prompt

Build me a small JavaScript library that makes page elements animate as they scroll into view.

I want it to be easy to use on a normal website, so someone can drop in a script tag and call something like ScrollReveal().reveal('.headline'), or install it from npm and import it in a module. The main goal is simple, smooth reveal animations for headings, sections, cards, and other content as they enter the viewport.

Please make it feel lightweight and reliable, with a clean public API, good defaults, and support for repeated use across a page. If you need to check any current browser behavior or docs online while building it, go ahead. Also include a basic demo page or example usage so it is obvious how to apply the effect to a few elements.