Reproduction

Steps to reproduce:

1. Open the URL https://material.angular.io/components/datepicker/examples
2. Open date range picker in example 1
3. Navigate to the selected date using keyboard arrow keys
4. Observe that when focus is on selected date , user cannot understand where the current focus is.

Expected Behavior

Provide a focus indicator or drop shadow in addition to the background color change

Actual Behavior

Focus indicator is not present for the selected state of date's present inside date range picker. Hence it is difficult for the users to know where the focus is

Environment

• Angular: 11.0.3
• CDK/Material: 11.0.3
• Browser(s): Chrome browser 90.0.4430.100
• Operating System (e.g. Windows, macOS, Ubuntu): Google Chrome OS