1680 by 1779 (one half of a 4k monitor)
I think the issue is that your hero section has a style of "width: 110vh", so it's 110% the height of the user's screen. On a browser that's set to fullscreen on a typical 16:9 aspect ratio monitor that will look fine, but when you've got a fancier set up that means you don't use fullscreen windows it breaks.
