Panel does not fit in Box Sizer put in Frame! !! !! !!

I am troubled...

I was making a wxPython calculator UI using wxFormBuilder I can't put wxPanel in wxFrame. .. ..

Problems that start with misunderstanding

I thought it was a wxPanel It seems that overseas Aniki was also worried about the same thing. Looking at the answer to that question, one screenshot ...

Oh, this is wxPanel

That was the case. It was a Panel, not a wxPanel. I misunderstood it because it is in Forms with Frame. So where is the correct wxPanel? ??

It was here.

It was in Contains.

Finally

I'm not the only one who makes such a mistake. .. ..