plastique style sheet, how to change custom parameter

[Michael_Levin]

Hi!
i use Plastique style sheep for an application.
If i want to change only font of QPushButton by stylesheet:

self.comment_btn.setStyleSheet('''QPushButton {font: bold 8px; }''')

self.comment_btn.setStyleSheet('''QPushButton {font: bold 8px; }''')

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everything works,
but if i change some parameter of plastique stylesheet:

self.comment2_btn.setStyleSheet('''QPushButton {font: bold 10px;  background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 #FF92BB, stop: 1 white);}''')

self.comment2_btn.setStyleSheet('''QPushButton {font: bold 10px;  background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 #FF92BB, stop: 1 white);}''')

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all other plastique style settings removes. How can i change only one, custom parameter of my style sheet? without loosing all others.