Button on mac is ok, but not show on window7

my code:

class MarkdownFrame(wx.Frame):
    """Markdown Please class, sub window."""
    def __init__(self):
        """Create a Frame instance"""
        wx.Frame.__init__(self, None, title="Markdown Please", size=(900, 800))

        # self.Maximize(True)
        self.Centre()

        #self.main_frame = mainframe
        #self.current_index = 0

        panel = wx.Panel(self, size=self.GetSize())

        # for vbox_cmd1
        url_param_label = wx.StaticText(self, -1, "Param:")
        self.url_param_text = wx.TextCtrl(self, -1, "", size=(300, -1))

        button_markdown = wx.Button(self, -1, label="Markdown")
        # button_markdown.SetDefault()
        # button_markdown.SetSize(button_markdown.GetBestSize())
        # button_markdown.SetToolTip("This is a Hello button...")
        button_reset = wx.Button(self, -1, label="Reset")
        # button_reset.SetDefault()
        button_tellme = wx.Button(self, -1, label="TellMe")
        button_close = wx.Button(self, -1, label="Close")

        vbox_cmd1 = wx.BoxSizer(wx.HORIZONTAL)
        vbox_cmd1.Add(url_param_label, 0, wx.ALIGN_LEFT)
        vbox_cmd1.Add(self.url_param_text, 0, wx.ALIGN_LEFT)
        vbox_cmd1.Add((5, 5))
        vbox_cmd1.Add(button_markdown, 0, wx.ALIGN_LEFT)
        vbox_cmd1.Add((5, 5))
        vbox_cmd1.Add(button_reset, 0, wx.ALIGN_LEFT)
        vbox_cmd1.Add((5, 5))
        vbox_cmd1.Add(button_tellme, 0, wx.ALIGN_LEFT)
        vbox_cmd1.Add((5, 5))
        vbox_cmd1.Add(button_close, 0, wx.ALIGN_LEFT)

        self.Bind(wx.EVT_BUTTON, self.OnMarkdown, button_markdown)
        self.Bind(wx.EVT_BUTTON, self.OnReset, button_reset)
        self.Bind(wx.EVT_BUTTON, self.OnTellMe, button_tellme)
        self.Bind(wx.EVT_BUTTON, self.OnClose, button_close)

        # for vbox_cmd2
        url_label = wx.StaticText(self, -1, "    URL:")
        self.url_text = wx.TextCtrl(self, -1, url, size=(800, -1))

        vbox_cmd2 = wx.BoxSizer(wx.HORIZONTAL)
        vbox_cmd2.Add(url_label, 0, wx.ALIGN_LEFT)
        vbox_cmd2.Add(self.url_text, 0, wx.ALIGN_LEFT)

        # for vbox_top
        self.text_multi_text = wx.TextCtrl(self, -1, "", size=(300, 200), style=wx.TE_MULTILINE)

        vbox_top = wx.BoxSizer(wx.VERTICAL)
        vbox_top.Add(vbox_cmd1, flag=wx.ALIGN_LEFT)
        vbox_top.Add((5, 5))
        vbox_top.Add(vbox_cmd2, flag=wx.ALIGN_LEFT)
        vbox_top.Add((5, 5))
        vbox_top.Add(self.text_multi_text, 1, wx.EXPAND)

        panel.SetSizer(vbox_top)
        panel.Layout()

Mac show:

windwos7 show:

first meet this button issue, need help.

The main reason is:
# panel = wx.Panel(self, size=self.GetSize())
panel = wx.Panel(self, -1)

And win7 interface now as:

The interface has obvious flaws

You should probably make all the widgets be children of the panel instead of the frame.

yes, now all is right.
My program error.
thanks thanks