MPP-3106: Fix "Learn more" tooltip going off screen on mobile devices

[rafeerahman]

This PR fixes MPP-3106.

Bug description

The "Learn more" tooltip for trackers removal can go off the screen in iOS and android devices.

Screenshot of fix

How to test

1. Login to premium relay account on a mobile device in Safari or Chrome
2. Select "Learn more" under the trackers removed stats box
3. Verify that the tooltip does not go out of bounds.

Checklist (Definition of Done)

• Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• Customer Experience team has seen or waived a demo of functionality.
• All acceptance criteria are met.
• Jira ticket has been updated (if needed) to match changes made during the development process.
• I've added or updated relevant docs in the docs/ directory
• Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.
• All UI revisions follow the coding standards, and use Protocol tokens where applicable (see /frontend/src/styles/tokens.scss).
• Commits in this PR are minimal and have descriptive commit messages.
• l10n changes have been submitted to the l10n repository, if any.

[jwhitlock]

Thanks @rafeerahman!