sizerLeft->Add(2, 2, 0, wxGROW | wxALL, 1); // spacer
sizerLeft->Add(btn, 0, wxALIGN_CENTRE_HORIZONTAL | wxALL, 15);
// middle pane
sizerLeft->Add(2, 2, 0, wxGROW | wxALL, 1); // spacer
sizerLeft->Add(btn, 0, wxALIGN_CENTRE_HORIZONTAL | wxALL, 15);
// middle pane