a.M. Blue Sleeveless Button-Down Shirt with Pockets (Medium?)

19” across chest 29” top to bottom (No labels, 1” wider than a similar shirt in Small, so assumed Medium) True size unknown (measurements also in photos). Fabric unknown, but feels like a quality polyester/chiffon. Functional pockets. Thick, but lightweight, well made. Purchased at a sample sale in NYC. *very small stain on right shoulder (pictured)* Questions? Leave a comment below!