WooCommerce: shipping option description

functions.php

<?php 
// Paste everything below this line to your child-theme's functions.php file.

// Transforms 
// >> Shipping Option Name (shipping option description): $99 
// to
// >> Shipping Option Name: $99<br>
// >> <small>shipping option description</small>
add_filter('woocommerce_cart_shipping_method_full_label', function($label, $method) {
    if (($open = strpos($label, '(')) !== false &&
       ($close = strpos($label, ')', $open+1)) !== false) {
        $desc = substr($label, $open+1, $close - $open - 1);
        $label = substr_replace($label, '', $open, $close - $open + 1);
        $label .= "<br><small>{$desc}</small>";
    }
    return $label;
}, 10, 2);