Hint: Think about exactly how each value calculates and distributes each item's share of the leftover space — as space fully surrounding each item individually, or as space split evenly among every gap position, edges included.

space-around gives each individual flex item an equal amount of space on both of its own sides, meaning each item effectively gets its own full margin-equivalent portion of space to its left and right — but two adjacent items each contribute their own adjacent half-portions of space between them, which combine to form one full-sized gap between items, while the outermost edges only receive one single item's own half-portion of space, with no neighboring item on that outer side to contribute a matching second half. This is exactly why space-around's edge gaps visually appear to be half the size of its between-item gaps, since the edges are structurally only getting one contributing half-portion instead of two combined halves. space-evenly, by contrast, doesn't calculate space on a per-item basis at all, it instead divides the total leftover space into equal-sized gaps positioned at every single gap location around and between all the items uniformly, including the two outer edges, which is precisely why every gap, edges included, ends up exactly equal under space-evenly, unlike the intentionally different edge-versus-between sizing that space-around's per-item calculation method produces.