Insert HTML into Responsive Header

I need the HTML for the email subscription box (contained in email-box.html) inserted into the responsive header of index.html where it says "email-box.html to go here". (Please see the attached project zip files)

The HTML for the email subscription box is already responsive, so all you will need to do is harmonize it with the HTML/CSS of index.html. Where the menu for index.html changes in the mobile menu, the email subscription box will need to be hidden.