protected boolean isCustomBackground( Color bg ) {
		return bg != background && (startBackground == null || bg != startBackground);
	}
Similar to BasicButtonUI.paint(), but does not use zero insets for HTML text,
which is done in BasicButtonUI.layout() since Java 19.
See https://github.com/openjdk/jdk/pull/8407
and https://github.com/openjdk/jdk/pull/8407#issuecomment-1761583430
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatButtonUI.java