Thick and Warm Sweater with accent on back

The sweater feels like it has been "double knit", with a dense, thick fabric - plain charcoal front, and two seafoam green vertical stripes up the back (the close-up photo colours are not correct - it is more charcoal than brown) - labelled as size L, but it looks like a small fit, so I have posted it as M - Sandwich brand - Viscose, cotton, polyamide blend - brand new, never worn - pit-to-pit across the front is 52 cm - back length from neck to bottom of waistband is 61 cm