Counts the sprite, the button's padding and border, the grid gap and the page and card padding, then checks that three columns either fit at 320px or that a media query has taken one away before they stop fitting. The arithmetic beats a remembered breakpoint: the number moves the moment anyone touches the sprite size or a padding, and the failure says what the grid needs against what the viewport has left. It counts chrome and not the unit names, so it is a floor and a browser is still what says the page does not scroll.