WooCommerce - Add Body Class

add_filter( 'body_class', 'custom_wc_product_cats_css_body_class' );

function custom_wc_product_cats_css_body_class( $classes ){
  if ( is_singular( 'product' ) ) {
    $current_product = wc_get_product();
    $custom_terms = get_the_terms( $current_product->get_id(), 'product_cat' );
    if ( $custom_terms ) {
      foreach ( $custom_terms as $custom_term ) {
        $classes[] = 'product_cat-' . $custom_term->slug;
      }
    }
  }
  return $classes;
}