It's also exactly how Firefox and Chrome's date pickers look. So they were probably to up their web compatibility game to look like everyone else and give users a more consistent UI
Some of these new (unified) UI elements are just awful.
My pet grievance is the range input, which is now filled by an accent color from the left (start) up to the selected value. Meaning, if you provide your users a range from -200 to +200 to select a value from, and a user selects a value of 2, this represents a selection of 202 units, which is apparently the real meaning of the number 2. (As is, Safari is the only major browser not participating in this nonsense.)
