Givebutter Integration into header

I am adding Givebutter integration in the form of donor buttons and a donation form. The way the integration works with a button is that clicking a button opens a modal window, so the user can make their donation without being directed away from the site. This is the behavior we want. While this works as expected in the body, I cannot see how to add this functionality to a button in the header. 

Hi,

What is your site url + Givebutter url/embed code, we can check easier