wxPython widget not centered vertically

I am trying to center a CheckBox widget vertically inside a panel. I cannot figure out why it's aligned to the top.

I had to create a Panel for the CheckBox because without that the background looks ugly (Windows 10 -- see second image)

Thanks for suggestions!

class wxUIE(wx.Frame):

    def __init__(self, parent, title):


        wx.Frame.__init__(self, parent, size=(800, 400), title=title)

        self.editorText = wx.TextCtrl (self, style=wx.TE_MULTILINE+wx.SUNKEN_BORDER+wx.TE_BESTWRAP)

        self.myBar = wx.TextCtrl (self, -1)
        # Checkbox
        self.myCheckBoxPanel = wx.Panel(self, size=(-1, 25))
        self.myCheckBox = wx.CheckBox(self.myCheckBoxPanel, label="Highlight",  style=wx.ALIGN_CENTER_VERTICAL)

        self.sizer = wx.BoxSizer(wx.VERTICAL)
        self.sizer2 = wx.BoxSizer(wx.HORIZONTAL)

        self.sizer.Add(self.editorText, 1, wx.EXPAND)

        self.sizer.Add(self.sizer2, 0, wx.EXPAND)
        self.sizer2.Add(self.myBar, 10, wx.EXPAND)
        self.sizer2.Add(self.myCheckBoxPanel, 0, wx.EXPAND)

        self.SetSizeHints(800,400)
        self.SetSizer(self.sizer)
        self.SetAutoLayout(True)
        self.Show()


# Run the program
if __name__ == "__main__":
    app = wx.App(False)
    frame = wxUIE(None, "My Edit Control")
    frame.Show()
    app.MainLoop()

CheckBox aligned to top of panel

CheckBox is aligned vertically correctly but the background sucks.