rahulde2007/Calcx-Pro-Calculator ? reverse-engineered prompt

Build me a polished calculator web app called Calcx Pro that feels fast, modern, and reliable on desktop and mobile.

It should have a standard mode for everyday math and a scientific mode for things like trig, logs, roots, powers, factorials, parentheses, percentages, and constants like pi and e. I want it to support keyboard input too, not just clicking buttons, and the display should handle backspace, clear, all clear, and chained expressions nicely.

Please also include memory buttons, a visible memory indicator, and a history panel that saves recent calculations, lets me tap one to reuse it, copy results, delete items, and export the history to CSV. Add light, dark, and system themes, save the user’s preferences, and make it work offline as an installable app. Keep it clean, high contrast, and accessible, with a responsive layout that works well on small screens.

If you need current docs for anything, look them up online as you build.