@Override
			public Dimension getMaximumSize() {
				// allow the button to fill whole button area height
				// see also BasicMenuUI.getMaximumSize()
				return buttonsFillVertically
					? new Dimension( super.getMaximumSize().width, Short.MAX_VALUE )
					: super.getMaximumSize();
			}
This panel paint a border at the top of the window in fullWindowContent mode,
if FlatLaf window decorations are enabled.
Only used on Windows 10.
<p>
This panel is not a child of the title pane.
Instead it is added by FlatRootPaneUI to the layered pane at a layer over all other layers.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTitlePane.java