Apply custom class to Gutenberg block element. View full tutorials at https://jeffreycarandang.com/extending-gutenberg-core-blocks-with-custom-attributes-and-controls/

apply-extra-class.js

/**
 * External Dependencies
 */
import classnames from 'classnames';

/**
 * Add custom element class in save element.
 *
 * @param {Object} extraProps     Block element.
 * @param {Object} blockType      Blocks object.
 * @param {Object} attributes     Blocks attributes.
 *
 * @return {Object} extraProps Modified block element.
 */
function applyExtraClass( extraProps, blockType, attributes ) {

	const { visibleOnMobile } = attributes;
	
	//check if attribute exists for old Gutenberg version compatibility
	//add class only when visibleOnMobile = false
	if ( typeof visibleOnMobile !== 'undefined' && !visibleOnMobile ) {
		extraProps.className = classnames( extraProps.className, 'mobile-hidden' );
	}

	return extraProps;
}

addFilter(
	'blocks.getSaveContent.extraProps',
	'editorskit/applyExtraClass',
	applyExtraClass
);

is it possible to add extraclass to core blocks ?