Agency scrolling to the right in Safari

I’ve been fiddling around with the Agency theme for a few days and am nearly ready to deploy the site. Today I discovered that I could scroll a bit to the right in Safari (9.1) and the Tech Preview. This issue doesn’t happen in the Vivaldi Browser, so it’s probably some Safari issue, but I can’t figure out what it is.

Probably should create an issue on the Agency theme repo:

I did, thanks.