It's because they calculate the "rounded corners" of the page with clamp() in CSS (which we don't yet support)
CODE:
--border-radius: clamp(var(--sp-4), 1.578vw, var(--sp-7d5));--border-radius-medium: calc(clamp(1em, 1.7vw, 1.7em)*1.2) ;--border-radius-small: calc(clamp(1em, 1.7vw, 1.7em)/2) ;