Mortgage repayment calculator - HTML, CSS, and JS

Styling the radio inputs was a bit difficult, as the styles that can be applied to default radio input are limited. I had to learn how to create keyboard accessible custom radio buttons.

I tried to search for help on how to format the input values(numbers) to show the commas, but i could not find a perfect solution. I would like to know how i can solve that, and also, is it possible to customize number inputs that allows users to enter values instead of the default one? I would really appreciate corrections and feedbacks on how i can better improve. Thank you