A full-height divider between two independently-sized layout regions, sourced from continuous-welded-rail breather switches: the seam's tapered-blade teeth interlock and slide apart as a rendered rail temperature swings the gap between 4px and 22px on a 14s cycle, actually resizing the element that sits between its neighbours rather than drawing over a fixed rule.
npx shadcn@latest add https://design.helpmarq.com/r/expansion-gap-breather.jsonexpansion-gap-breather