Did you change it recently. I currently checked your site here in Safari and it looks fine to me. I tried testing it in all version of mac from online testing tool, but the Signup popup blocked that area. Any chance you can disable that for today. So that we can check it ?
We seem to have narrowed it down to iOS9 mobile users that are having the problem.
I had a look on Browserstack and couldn’t work out to use the iOS9 emulator. They seem to suggest they have it on their site, but couldn’t spot it in the list.
“One of our devs just asked about this while in the Apple retail store and they’re saying it’s a fairly widespread problem they’ve been seeing…so I’m guessing I’ll just have to wait for them to roll out a fix.”