Copy Button Code (7.1)

Site URL: https://accordion-pear-2lep.squarespace.com/

I have a code plugin on page https://accordion-pear-2lep.squarespace.com/join and am trying to figure out how to add a button into the code (trying to add it into the box under Stage One)

I can't find a way to copy a button code -- I have a button that I want to embed into the code on page: /button

I've tried my hand at isolating the code on developer tools, but have no idea what I'm looking for there and I've messed the form up a few times. 

How do I get the code for this button? 

https://accordion-pear-2lep.squarespace.com/

Password is: Davidisawesome#1