Polish groupedItem button

[luixxiul]

Test plan

#9357 (comment)

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Describe the issue you encountered: Polish groupedItem button.

Remove margin from browserButton and add it to groupedItem. A button as such does not require margin. Since the button requires the margin when it is grouped with another button in the same wrapper, adding margin to BrowserButton with groupedItem is a better solution than adding it to all buttons, some of whose margin would be canceled with margin: 0.

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