saurav7747/Nexus ? reverse-engineered prompt

Build me a simple demo web app called Nexus that feels polished on desktop and mobile.

I want it to load fast, look clean, and work like a small installable app with an app icon, manifest, and offline support so it can still open if the internet drops. Keep the layout responsive, give it a modern landing screen, and make the main interaction easy to understand without needing instructions.

If there are any missing pieces, wire them up so the page actually works end to end, and use current docs online if you need to check anything. Keep the experience lightweight and smooth, and make sure the styling, scripts, and service worker all work together cleanly.