Currently scroll snapping algorithms selects closest point from all snap areas ignoring whether they are visible in viewport or not.

The spec requires us to limit valid candidates to those visible [1]. Here is the relevant text:

"Since the purpose of scroll snapping is to align content within the viewport for optimal viewing, a scroll container cannot be snapped to a snap area if no part of it is within the snapport. For example, a snap area is top-aligned to the snapport if its top edge is coincident with the snapport’s top edge; however, this scroll position is nonetheless not a valid snap position if the entire snap area is outside the snapport (because the required alignment, though satisfied, would not be relevant to the viewer)."



[1] https://drafts.csswg.org/css-scroll-snap-1/#snap-scope