YasirPY/Calculator ? reverse-engineered prompt

Build me a simple calculator web app that works in the browser and feels clean and easy to use.

I want a basic calculator with a display and buttons for numbers, plus the common operations like add, subtract, multiply, and divide. It should also have clear and equals, and let me type or click the buttons to do calculations. Make sure it handles normal calculator behavior in a sensible way, like chaining operations, clearing the current entry, and showing the result neatly.

Keep the design simple but polished, with good spacing, readable buttons, and a layout that works well on a phone or desktop. Use the existing HTML, CSS, and JavaScript files, and make everything work as a small self contained page. If you need to check anything, look up current browser best practices online.