Nothing-dot-exe/Age-calculator — reverse-engineered prompt

Build me a simple fun age calculator as a single page website using plain HTML, CSS, and JavaScript. I want someone to type their birthday in DD/MM/YYYY format, and the input should automatically add the slashes while they type so it feels easy to use. They should be able to click a button or press Enter to calculate.

After they submit, show a few funny loading messages for a moment, then display their exact age in years, months, and days. Also show a live countdown to their next birthday with days, hours, minutes, and seconds updating on the page.

Make the design feel modern and playful, with a nice gradient background, a centered card layout, smooth spacing, and small interactive touches. Add a GitHub link somewhere near the bottom with a hover effect that uses GitHub style colors. Keep everything clean, responsive, and easy to understand in one HTML file if possible.