How to get calendar_today_outlined icon for angular material datepicker?

According to the documentation, https://api.flutter.dev/flutter/material/Icons/calendar_today_outlined-constant.html

calendar_today_outlined icon is shown as:

But when I use it in example

<mat-icon #pickerSingleIcon>calendar_today_outlined</mat-icon>


I get the header filled:

This confused me why the specified caleander_today_outlined icon is shown the same as calendar_today.

Wonder how to get the outlined icon for the calendar?

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