Add padding around showAllWrap button

[luixxiul]

Fix #8869

Auditors:

Test Plan:

1. Run npm run add-simulated-synopsis-visits until "Show All" button appears
2. Open about:preferences#payments
3. Disable payments
4. Make sure there is 40 px padding under the panel
5. Enable payments
6. Make sure there is 40 px padding under "Show All" button

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[cezaraugusto]

++