Good job so far, it feels very lightweight and simple. It works well with different input devices, but the accessibility for screen readers could be improved:
* The first day immediately gets focused when opening the datepicker. It might be a bit confusing to just hear a number.
* There's enough space to spell the months in full.
* Use semantic abbrevations for weekdays, e.g. `<abbr title="Monday">Mo</abbr>`.
* Use `label`s which refer to the corresponding `select`.
* Use `table` instead of `div`s for the calendar view.
* Use (hidden) text instead of the `title` attribute in buttons.
Furthermore:
* Try using more unique classes for your elements, e.g. '.aeon-datepicker__select' instead of '.select'.
* `cursor: pointer` for buttons would be helpful to see how large the click area is.
* The first day immediately gets focused when opening the datepicker. It might be a bit confusing to just hear a number.
* There's enough space to spell the months in full.
* Use semantic abbrevations for weekdays, e.g. `<abbr title="Monday">Mo</abbr>`.
* Use `label`s which refer to the corresponding `select`.
* Use `table` instead of `div`s for the calendar view.
* Use (hidden) text instead of the `title` attribute in buttons.
Furthermore:
* Try using more unique classes for your elements, e.g. '.aeon-datepicker__select' instead of '.select'.
* `cursor: pointer` for buttons would be helpful to see how large the click area is.