Html code used for calendar popup

Can anyone provide the html code of the calendar date-picker popup used in manager date fields?
I want to edit it into a custom field in a sales -line item. This for multiple lines on a taxi-cab weekly Trips Invoice to a specific customer.

Please disregard this request. I’ve decided it’s much simpler to just edit the invoice manually and alter the data as necessary.
Just as a FYI, I DO have a date-picker custom field working well on a customized invoice but that’s different to what I originally asked.
Thanks all who viewed. Sorry for the time-waste.