bug(mat-expansion-panel): In high contrast mode, keyboard focus not visible around panel

[dwaynelavon]

Reproduction

Stackblitz: https://stackblitz.com/angular/drrqqddrvej?file=src%2Fapp%2Fexpansion-overview-example.ts

Expected Behavior

What behavior were you expecting to see?

1. Enable Windows high contrast mode in settings
2. Open Firefox
3. Create a mat-expansion-panel (Stackblitz above)
4. Use keyboard to tab to the expansion panel and observe focus indicator

Actual Behavior

What behavior did you actually see?
Keyboard focus indicator is not visible around expansion panel

Environment

• Angular: 11.0.3
• CDK/Material: 11.0.3
• Browser(s): Firefox
• Operating System (e.g. Windows, macOS, Ubuntu): Windows

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