wxpython:用另一个wx.panel覆盖wx.panel，但新面板不能正确调整大小

import wx

class MainPanel(wx.Panel):
    def __init__(self, parent):
        wx.Panel.__init__(self, parent)
        
        # 创建主面板上的控件
        self.label = wx.StaticText(self, label="Main Panel")
        
        # 创建Sizer并添加控件
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.label, 0, wx.ALL, 5)
        self.SetSizer(sizer)

class OverlayPanel(wx.Panel):
    def __init__(self, parent):
        wx.Panel.__init__(self, parent)
        
        # 创建覆盖面板上的控件
        self.label = wx.StaticText(self, label="Overlay Panel")
        
        # 创建Sizer并添加控件
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.label, 0, wx.ALL, 5)
        self.SetSizer(sizer)

class MyFrame(wx.Frame):
    def __init__(self):
        wx.Frame.__init__(self, None, title="wxPython Overlay Example")
        
        # 创建主面板和覆盖面板
        self.main_panel = MainPanel(self)
        self.overlay_panel = OverlayPanel(self.main_panel)
        
        # 设置Sizer来管理面板布局
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.main_panel, 1, wx.EXPAND)
        self.SetSizer(sizer)
        
        # 绑定事件处理函数
        self.Bind(wx.EVT_SIZE, self.on_size)
    
    def on_size(self, event):
        # 调整覆盖面板的大小以适应主面板
        size = self.main_panel.GetSize()
        self.overlay_panel.SetSize(size)
        event.Skip()

if __name__ == "__main__":
    app = wx.App()
    frame = MyFrame()
    frame.Show()
    app.MainLoop()