This is a lightweight buttonfront blouse from J Crew.
It’s done in a blue and white floral pattern against a black background. The neckline has two attached straps that can be tied into a bow. The long sleeves have a button closure, and there is a slightly rounded bottom.
It is semi-sheer when held up to the light.
100% polyester, machine washable.
Size M, the chest is approx 21” across and the length to center is about 26”.