codrops/ThumbFullTransition ? reverse-engineered prompt

Build me a small demo site with that thumbnail to full width image transition effect. I want a clean article style layout where a small image card expands smoothly into a wide hero image when you click it, then feels like it enters the article view in a classy way.

Please make the animation polished and fluid, using the same kind of motion quality as the Codrops demo, with responsive behavior so it still looks good on mobile and desktop. Keep the page simple and focused on the effect, with some sample article content and a few image placeholders so I can see the transition in context.

Use plain JavaScript and CSS, and if animation helpers make it easier, use GSAP. Make it easy to run locally with a dev server and build it for production. If you need current docs or best practices for the animation part, look them up online first.