Regression: margin between buttons on backup brave wallet dialog

[luixxiul]

Test plan

#8737 (comment)

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Describe the issue you encountered: #8560 (comment)

As I removed .paymentsContainer the margin between the buttons on "Back up your Brave wallet" dialog have regressed. The specification here seems to be no longer applied: https://github.com/brave/browser-laptop/blob/master/less/button.less#L180

Since on the other dialogs the margin exists, I believe something is inconsistent between them. I'll tackle that.

• Brave Version (revision SHA): 0.15.3 preview 3

• Steps to reproduce:

  1. Open about:preferences#payments
  2. Open advanced settings
  3. Click "Back up your wallet"

• Actual result:
  

• Expected result: there should be margin between each button

• Extra QA steps:
  1.
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• Screenshot if needed:

• Any related issues:

[luixxiul]

I misunderstood the issue but found the solution anyway. I'll push a fix soon.