Hello,
Thanks for the topic. Please provide us with full access, because we can’t check your admin panel.
1. In 4.16 theme version Menu options were moved into popup https://prnt.sc/idhhcf so to be able to see all menu settings, you need to click on “8Theme Page Options”.
2. Please see screenshots – http://prntscr.com/j0lx8x > https://prnt.sc/j0lxhy
3. Find the code in our documentation – https://xstore.helpscoutdocs.com/article/66-mailchimp-form-custom-styles
Regards