Add custom block styles - Easily enhance the block editor with custom block styles. https://www.damiencarbery.com/2022/04/add-custom-block-styles/

dcwd-custom-block-styles.css

/* Highlight paragraph style. */
p.is-style-highlight, .editor-styles-wrapper p.is-style-highlight { font-size: 180%; }

/* Rotated image style. */
.is-style-rotated img { transform: rotate(180deg); }

/* Group block Info and Warning styles. */
.is-style-group-info, .is-style-group-warning { margin: 0 0 10px; }
.is-style-group-info, .is-style-group-warning { padding: 2em; min-height: 35px; }
.is-style-group-info strong, .is-style-group-warning strong { color: #000000; font-weight: bold; }
.is-style-group-warning p:last-child, .is-style-group-info p:last-child { margin-bottom: 0; }

.is-style-group-info { border: 1px solid #e2e2ba; }
.is-style-group-warning { border: 1px solid #e0b1b1; }
.is-style-group-info { color: #ada771; background: #f9f9dc; border: 1px solid #fbfbef; }
.is-style-group-warning { color: #ad7676; background: #ffd9d5; border: 1px solid #fceeec; }

dcwd-custom-block-styles.php

<?php
/*
Plugin Name: Add custom block styles
Plugin URI: https://www.damiencarbery.com/2022/04/add-custom-block-styles/
Description: Easily enhance the block editor with custom block styles. Inspired by https://briangardner.com/border-block-style/.
Author: Damien Carbery
Version: 0.4
*/


// See list of core blocks at: https://developer.wordpress.org/block-editor/reference-guides/core-blocks/


// Add custom styles to some core blocks.
function dcwd_register_custom_block_styles() {
	$style_handle = 'dcwd-custom-block-styles';

	wp_register_style( $style_handle, plugins_url( 'dcwd-custom-block-styles.css', __FILE__ ) );

	// Block themes do not automatically enqueue the stylesheet when the custom block
	// style is used. This appear to be a core bug (#55184).
	// The workaround is to always enqueue the file for those themes.
	if ( wp_is_block_theme() ) {
		wp_enqueue_style( $style_handle );
		error_log( 'wp_enqueue_style $style_handle' );
	}

	// Add 'Highlight' stye to paragraph block.
	register_block_style(
		'core/paragraph',
		array(
			'name'  => 'highlight',
			'label' => 'Highlight',
			//'inline_style' => 'p.is-style-highlight { font-size: 180%; }',
			'style_handle' => $style_handle,
		)
	);

	// Add 'Rotated' style to Image block
	register_block_style(
		'core/image',
		array(
			'name'  => 'rotated',
			'label' => 'Rotated',
			//'inline_style' => '.is-style-rotated img { transform: rotate(180deg); }',
			'style_handle' => $style_handle,
		)
	);

	// Add 'Info' style to Group block
	register_block_style(
		'core/group',
		array(
			'name'  => 'group-info',
			'label' => 'Info',
			'style_handle' => $style_handle,
		)
	);
	// Add 'Warning' style to Group block
	register_block_style(
		'core/group',
		array(
			'name'  => 'group-warning',
			'label' => 'Warning',
			'style_handle' => $style_handle,
		)
	);

}
add_action('init', 'dcwd_register_custom_block_styles' );


// Enqueue the CSS file so that the styles can be seen in the block editor.
add_action( 'enqueue_block_editor_assets', 'dcwd_enqueue_block_editor_styles' );
function dcwd_enqueue_block_editor_styles() {
    wp_enqueue_style( 'dcwd-custom-block-styles', plugin_dir_url( __FILE__ ) . 'dcwd-custom-block-styles.css' );
}