Responsive age calculator with HTML, CSS, AND JAVASCRIPT

This is an HTML code for an age calculator app. It contains a form that allows users to input their birth date, and a button that triggers a JavaScript function to calculate their age. The app displays the result in the format of years, months, and days. The app's user interface is responsive to different screen sizes, with the layout adjusted accordingly. The app also has a style.css file that defines the app's styles.

Validating the inputs with JavaScript was challenging, i tried my best but I didn't implement all that is required, i was able to validate the input for empty or NaN input but I couldn't validate for invalid date value (e.g. when a value more than 31 or 30 is inputted as the case may be for the day of the month, when a value more than 12 is inputted for the month, and when a value more than 2023 is provided for the year.) I would appreciate any help in this regard.