You already have that?
They both have the same function but are just styled a little differently. It should be a relatively easy matter to put your form elements inside the code I posted and add a bit of styling to match the amazon example?
What is is exactly that you can’t do?
The thread was about adding a radio button which I have shown one way for you to do it. You could indeed style the radio button differently if you styled an inner element of the label instead.
Here’s a start:
Note that the amazon site is more sophisticated and uses javascript to toggle the accordion with a fallback form post is js is disabled.