get_block_editor_theme_styles()

function get_block_editor_theme_styles() {
	global $editor_styles;

	if ( ! GC_Theme_JSON_Resolver::theme_has_support() ) {
		$styles = array(
			array(
				'css'            => 'body { font-family: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Oxygen-Sans,Ubuntu,Cantarell,"Helvetica Neue",sans-serif }',
				'__unstableType' => 'core',
			),
		);
	} else {
		$styles = array();
	}

	if ( $editor_styles && current_theme_supports( 'editor-styles' ) ) {
		foreach ( $editor_styles as $style ) {
			if ( preg_match( '~^(https?:)?//~', $style ) ) {
				$response = gc_remote_get( $style );
				if ( ! is_gc_error( $response ) ) {
					$styles[] = array(
						'css'            => gc_remote_retrieve_body( $response ),
						'__unstableType' => 'theme',
					);
				}
			} else {
				$file = get_theme_file_path( $style );
				if ( is_file( $file ) ) {
					$styles[] = array(
						'css'            => file_get_contents( $file ),
						'baseURL'        => get_theme_file_uri( $style ),
						'__unstableType' => 'theme',
					);
				}
			}
		}
	}

	return $styles;
}