utilities.php

<?php

/**
 * This function appends a class to the body depending on the environment.
 *
 * @param array $classes current body classes.
 *
 * @return array $classes any modification to the class array.
 */
function tgf_add_environment_class( $classes ) {

	if ( WP_LOCAL ) {
		$classes[] = 'env--local';
	}

	if ( WP_STAGING ) {
		$classes[] = 'env--staging';
	}

	if ( WP_PRODUCTION ) {
		$classes[] = 'env--production';
	}

	return $classes;
}
add_filter( 'body_class', 'tgf_add_environment_class' );