[Mobile Promotion] The "Get it on Google Play" and "Download on the App Store" buttons are not highlighted when focused using keyboard navigation

[SoftVision-CosminMuntean]

[Affected Versions]:

• Lockwise 2.2.0-alpha
• Firefox 67 and up

[Affected Platforms]

• All Windows
• All Mac
• All Linux

[Perquisites]

• Have the latest Firefox 67 version installed.
• Have the Lockwise 2.2.0 - alpha extension installed.
• You are signed with a FxA account.

[Steps to reproduce]:

1. Open the Firefox browser with the profile from prerequisites.
2. Click the "Lockwise" toolbar button and click the "Open Lockwise" button from the doorhanger.
3. Press the "Tab" key until the "Get it on Google Play" is focused.
4. Observe the button.

[Expected results]:

• The became highlighted when it is focused.

[Actual results]:

• The button is not highlighted even if it is focused.

[Notes]:

• Attached a screen recording of the issue: