@Override
	protected int getTabLabelShiftX( int tabPlacement, int tabIndex, boolean isSelected ) {
		if( isTabClosable( tabIndex ) && getRealTabRotation( tabPlacement ) == NONE ) {
			int shift = closeIcon.getIconWidth() / 2;
			return isLeftToRight() ? -shift : shift;
		}
		return 0;
	}
The content border insets are used to create a separator between tabs and content.
If client property JTabbedPane.hasFullBorder is true, then the content border insets
are also used for the border.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTabbedPaneUI.java