The root <svg> element has attributes height and width that have values appropriate to 100% scaling. This means when zoomed out (<100%) the browser displays a bigger page than necessary and when zoomed in (>100%) elements outside the page are not displayed.

The function scaleGraphic() needs to adjust those attribute values on the <svg> element. Probably the easiest way to do this is to pass them in to scaleGraphic() as arguments and supply them specifically when writing the <g id="scaleGroup"> group of elements.