Boubaker-Soltani/Web02_step4 ? reverse-engineered prompt

Build me a simple web calculator app that looks clean and works in the browser.

I want a page where someone can enter numbers, choose an operation, and तुरंत see the result without the page feeling clunky. Please make the front end easy to use and nicely styled, and keep the behavior in JavaScript so it feels responsive. On the backend, use PHP to handle the calculation and save the results so there is a basic history of what was done.

I also want a way to export the saved calculations, so I can download or copy the history when needed. If you need to check current best practices or docs for anything, go ahead and look them up online. Keep it simple, practical, and working end to end.