from PySide6.QtWidgets import QMainWindow, QWidget, QVBoxLayout, QSpinBox, QApplication

class SpinWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        w = QWidget(self)
        self.setCentralWidget(w)

        s1 = QSpinBox(self)
        s2 = QSpinBox(self)
        s2.setStyleSheet(" ")

        layout = QVBoxLayout(w)
        layout.addWidget(s1)
        layout.addWidget(s2)

if __name__ == "__main__":
    app = QApplication()
    app.setStyle("fusion")
    sw = SpinWindow()
    sw.show()
    app.exec()