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Here's a demo GUI that is built up from panels that contain multiple controls. Each panel is colored uniquely so that they are clearly differentiated from each other. Also, each panel was designed to have space borders on all edges of the panels so that controls from adjacent panels would be a bit separated from each other. In most real-world GUIs, the panels would have the same background color and the panels would not be labeled with their own class names.
Each panel holding just a single control does not necessarily have to have a StaticText used as a label to identify the particular purpose of the associated control. Some controls like the RadioBox already have label functionality built into them. Buttons are naturally self-labeling and don't need to be contained within a panel at all.
Only BoxSizers are used to arrange everything, of course.