Multi colored vest by “fundamental things” with no size listed

There isn’t a size for this item but it fits like a men’s small, it is pre-owned and in amazing condition with no materials listed Collar to bottom 17 ⅝” | waist 18 ⅞” | chest 18 ⅛” Size Guide: Collar to Bottom: Back of garment collar (bottom stitching) to the very bottom of garment Sleeve: Center Back of bottom of collar, to end of sleeve) Waist (of shirt): Horizontal length of the most narrow part of shirt Chest: Horizontal Measurement of under armpit seam to under armpit seam