NBD Revolve Toula Ribbed Long Sleeve Front Cutout Mock Neck Sweater Top. Revolve calls it a sweater on their website, but it's not super thick. More a lightweight ribbed sweater-ish material. In excellent condition. No flaws, pilling or stains.

Size: XS
Armpit to armpit: 9.25" (has lots of stretch- easily to 13")
Shoulder to hem: 17.5"