Okay, here's what I figured out: in the 4th tab, you've changed the font-size of the heading "What am I looking for" from 70 to 45. This reduces the size of that div, which is allowing the overlap. If you change the font-size of the div for A little bit more, too, in order to get it on one line, you'll notice that the fourth tab makes an unwelcome appearance at the bottom of the third tab. It's very strange.
This was an oversight on my part; I used the font-size of the banner section to create the height of the div, instead of fixing it in place. I didn't anticipate people wanting longer titles there and needing to change the font.
I believe there's a simple fix: add a fixed height to the div where you changed the font size. I picked 90px at random and it worked in my test run, but you might want to play around with that number and see how it pushes everything else around on the page. I was just looking to make sure it stopped the overflow. Shouldn't take you 5 minutes to fix it.
Just add that to the div and let me know how it goes!