protected boolean isWindowMaximized( Component c ) {
			Container parent = c.getParent();
			return parent instanceof Frame && (((Frame)parent).getExtendedState() & Frame.MAXIMIZED_BOTH) == Frame.MAXIMIZED_BOTH;
		}
Window border used for non-native window decorations.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatRootPaneUI.java