What’s causing this on a large desktop display? I haven’t played with css today, but I’m seeing a gap above Section 1 when I refresh the browser:

but it goes away when I scroll down even one pixel and then back to the top of the page:

I’ve adjusted Section padding and gap element, but nothing fixes it. I can prevent Section 1 from displaying on a large desktop display, and then the same thing happens with Section 2. The gap goes away as soon as I resize the browser down to a small desktop size or below. The DS in the video means that the visible Section is only marked to display on a small desktop display.
Here’s a video of it in action:
http://screencast-o-matic.com/watch/cbQthEIUrk