:: detour to site, quick, before link is deleted ::
Ouch. You've got five external stylesheets, wads of separate CSS declarations-- including at least one in the <body>-- AND inline styles. Get that all cleaned up and organized, and you may well find that the problems fix themselves.
:: further detour to Web Inspector, followed by downloading page and fine-tooth-combing CSS ::
Well. That's an hour of my life I'll never see again.
At first glance, the problem seemed to be in the social-media icons. Comment them out and the problem goes away. Leave them in, and the social-media bar behaves as if it were set for position: relative with a substantial left-offset.
But the real problem is
The problem only manifests itself if the ul has visible content-- here, the icons.
Yes, OK, so I was mistaken. Not a left offset but a negative right offset.
In short: The page is doing exactly what you've told it to do ;)