How to make the size of the parent widget not adjust to the child?

Question

I want the child widget to just appear in the center of the parent widget with a horizontal pink stripe. But the widget of the parent becomes very small.

from PySide6 import QtWidgets, QtGui
import sys


class WidgetA(QtWidgets.QWidget):
    def __init__(self):
        super(WidgetA, self).__init__()
        self.wb = WidgetB()
        vbox = QtWidgets.QVBoxLayout()
        hbox = QtWidgets.QHBoxLayout()
        hbox.addWidget(self.wb)
        vbox.addLayout(hbox)
        self.setLayout(vbox)


class WidgetB(QtWidgets.QWidget):
    def __init__(self):
        super(WidgetB, self).__init__()
        palette = self.palette()
        palette.setColor(QtGui.QPalette.Window, QtGui.QColor("#ff00ff"))
        self.setPalette(palette)


app = QtWidgets.QApplication()
window = WidgetA()
window.show()
sys.exit(app.exec())

If I have not written something, or something is not clear in my question, then ask, I will supplement it.