functions.php

<?php 
// Add below code to theme functions.php to create the bug/button-styling block.
// Ref: https://core.trac.wordpress.org/ticket/52555

add_action(
	'init',
	function() {
		wp_register_script( 'bug-button-styling', '', array( 'wp-blocks', 'wp-element', 'wp-server-side-render' ), '1.0', true );
		wp_enqueue_script( 'bug-button-styling' );
		wp_add_inline_script(
			'bug-button-styling',
			"
				( function( blocks, element, serverSideRender ) {
					blocks.registerBlockType( 'bug/button-styling', {
						title: 'Bug Button Styling',
						category: 'common',
						edit: function() {
							return element.createElement( serverSideRender, { block: 'bug/button-styling' } );
						}
					} );
			}(
				window.wp.blocks,
				window.wp.element,
				window.wp.serverSideRender
			) );
		"
		);
		register_block_type(
			'bug/button-styling',
			array(
				'editor-script'   => 'bug-button-styling',
				'render_callback' => function() {
					return '<div class="wp-block-button"><a href="#never-visited" class="wp-block-button__link">Link styled as a button</a></div>';
				},
			)
		);
	}
);