margin changes when payments is enabled and disabled

[luixxiul]

Test plan

#10154 (comment)

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Describe the issue you encountered: margin between the title wrapper and the content changes when payments is enabled and disabled.

This is due to that margin is not offset when the element is styled with float.

• Brave Version (revision SHA): master branch

• Steps to reproduce:

  1. Open about:preferences#payments
  2. Enable and disable Payments

• Actual result: the margin between the title wrapper and the content changes

• Expected result: it should not change

• Any related issues:

[luixxiul]

fyi I referred this document (written in Japanese) to find the issue: http://kojika17.com/2012/08/margin-of-css.html

It is a thorough analysis on the relationship between margin and flex.

[luixxiul]

Modified the milestone based on #10154 (comment).