Hello, I can see that you have done so great. but you should handle errors and states. you didn't do that. I just completed this project you can check it. I have added some extra features.
This is my first project using JavaScript.
What took the most time was the implementation of the function to check all exceptions that could occur during calculations (such as a leap year, the current year, but the month or day is less, how many days are there in a month).
I really enjoyed implementing this project.
I'm not really sure how well the DOM was implemented in this project, but since this was the first work using something other than HTML, SCSS I think it was a good result.
Many design elements had to be modified, as I encountered some difficulties and could not figure out how to solve them.
If you have comments on the code, I will be happy to read them, because this will allow me to grow as a Frontend developer