Hi,
Is this mobile Safari or Desktop safari? I assume it is the mobile version again?
That was a known problem a very long time ago with very old safari browsers, where the background clipped through the container element. It should not happen anymore. I am not sure if there is a way to get around that, as it should not be happening in the first place.
The solution to the old issue was setting an explicit overflow, but the thing is, that it is set already correctly.
Are you zoomed in on the device by any chance? Zooming will break borders.