The school School Uniform from Mototsu high school from Yurucamp.
It's a Serafuku consisting of a dark Blue Sailor Collar with a White Neckerchief, a long-sleeved Yellow Sweater a plaid dark blue/grey pleated Miniskirt, a Black Pantyhose and brown Loafers.
Since the manga/anime takes place during winter it's unclear if there is a summer version of the uniform, although flashbacks from middle school show characters wearing a short-sleeved white shirt.