seanbuckle/age-calculator — reverse-engineered prompt

Build me a polished age calculator web app. It should let someone enter their day, month, and year of birth, then show their exact age in years, months, and days.

Please make the date handling really reliable. It should reject impossible dates like April 31, February 29 on non leap years, empty fields, out of range days or months, and years in the future. Show clear inline error messages that are accessible and easy to understand.

The app should feel like a finished Frontend Mentor style project, with a clean responsive layout, light and dark mode that follows the user’s system theme, and a small animated count up effect when the result appears. Save the user’s last entered date in the browser so it comes back after a refresh.

Use TypeScript with Deno, SCSS, and simple browser storage. Keep the code tidy and maintainable, and make sure it runs locally with a Deno dev command.