Age calculator using vanilla Js

Looks good however the styling is broken on mobile. It does seem like you did add some styling for smaller screens however you used pixels to hard set the width and height values. You want to avoid using pixels in this way. It is far better practice to use rem or percentage(%).

A browser extension that helps me for testing my app on mobile is called Mobile FIRST. It can simulate phone screens and gives a preview of what your site will look like on a specific device.

Also in your body you have all of the main content wrapped in a section element. Make sure you wrap your main content in a <main> element for better semantics and SEO.

Hope this helps. Good luck coding!