bug(MatTabNav): scrollable MatTabNav bug

[tworry]

Reproduction

Use StackBlitz to reproduce your issue:

• https://stackblitz.com/edit/angular-b4mepp?file=src/styles.scss

Steps to reproduce:

1. set MatTabNav [disablePagination]="true"
2. change mat-tab css in style.scss
3. add more tab-link to make the MatTabNav scrollable
4. sroll to the end,and click the last link

Expected Behavior

the clicked link is active, the scroller is not changed

Actual Behavior

the MatTabNav is back to the start,and the clicked link is not active,just focused

Environment

• Angular:12.1.2
• CDK/Material:12.1.1
• Browser(s):chrome 91.0.4472.77
• Operating System (e.g. Windows, macOS, Ubuntu): Windows

[crisbeto]

First of all, this isn't something we support since you're overriding the built in styles.

That being said, there's an existing PR that should fix your issue too #21911.

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