...see you meant the gap between the text and the underline... Not sure you can do that, after a quick google search.
actually, i think you're right. i went back to check a squarespace site i thought i had negatively adjusted the underline value, but it wasn't negative. quick test showed negative value's don't work unfortunately. i think it's just this japanese font that has such a huge built-in gap defined for where the border is supposed to go.
i'm not quite how to apply then style a link span. i would guess i maybe add it to "custom a attributes" but then, no idea how i might select that within the webflow UI as a style. so, might just look for an alternate design method. thanks!