Active Tek Gear cut out back tank top best for S

Gently preowned, no flaws to note. Active, athletic, sports, yoga, run, fitness, workout, moisture managing cut out/cutout back strappy tank top. Built in bra, not padded. Actual size M but I find it to fit better size S, I usually go size up in similar fitted styles. Very dark gray or dusty black. Possibly the design on a side could be reflective. Measures 16 inches underarm to underarm flat and about 25 long.