div class="custom-header no-bg-img"

Hi,
On posts, pages and archives, there’s a huge gap between the header and the content which I can’t seem to remove. On mobile this gap is really significant. I don’t have a background image for the header, so I don’t think this is causing the problem.
Here’s one of the pages so you can see the issue: http://www.jamiesfamilykitchen.com/sign-up/
How can I remove this spacer?
Thanks in advance,
Tom