Filter field classes

You can filter the class applied to each product extra field, just use the pewc_filter_single_product_classes filter:

	function prefix_filter_single_product_classes( $classes, $item ) {
	$classes[] = 'my-new-class';
	return $classes;
	}
	add_filter( 'pewc_filter_single_product_classes', 'prefix_filter_single_product_classes', 10, 2 );

The filter also passes the $item object so you can do conditional stuff based on the item.