Add margin-left to the notification button

[luixxiul]

• 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).

The value is based on padding-top here: https://github.com/brave/browser-laptop/blob/master/less/notificationBar.less#L16

Addresses #3939

Auditors: @ayumi

Test Plan:

1. Go to https://trac.torproject.org/projects/tor
2. Log in with your username and password
3. Change the window size

[ayumi]

Thanks! Tried it out locally, looks sweet ++ 🎁