iOS Calculator Clone

Recreate the Apple iOS calculator as a single HTML file using only HTML, CSS, and vanilla JavaScript — no libraries or CDNs.

Match the iOS look as closely as you can:
- Dark background
- Round buttons
- Orange operator keys (÷ × − + =)
- Light-grey top-row keys (AC, +/−, %)
- The "0" key spanning two columns
- This layout, top to bottom: [AC, +/−, %, ÷] [7,8,9,×] [4,5,6,−] [1,2,3,+] [0, ., =]

The calculator must actually perform the calculations correctly. Return only the full HTML file content and nothing else.