public void setShowContentSeparators( boolean showContentSeparators ) {
		putClientPropertyBoolean( TABBED_PANE_SHOW_CONTENT_SEPARATOR, showContentSeparators, true );
	}
Specifies whether the separator between tabs area and content area should be shown.
flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/components/FlatTabbedPane.java