Block specific custom styles

wds_block_specific_custom_styles.php

<?php
function my_theme_register_button_styles() {
    wp_register_style(
        'my-theme-button-styles',
        get_stylesheet_directory_uri() . '/button-styles.css',
        array(),
        filemtime( get_stylesheet_directory() . '/button-styles.css' )
    );

    register_block_style(
        'core/button',
        array(
            'name' => 'my-theme-button-style',
            'label' => __( 'My Button Style', 'my_theme' ),
            'style_handle' => 'my-theme-button-styles',
            'style' => 'my-theme-button-style',
        )
    );
}
add_action( 'init', 'my_theme_register_button_styles' );