function setCookie(name, value, hours) {
  var expires = "";
  if (hours) {
    var date = new Date();
    date.setTime(date.getTime() + (hours*60*60*1000));
    expires = "; expires=" + date.toUTCString();
  }
  document.cookie = name + "=" + (value || "")  + expires + "; path=/";
}

btn.onclick = function() {
  setCookie("interior", interior.currentColor, 0.1);
}

add_filter('woocommerce_add_cart_item_data','custom_add_item_data',10,3);

function custom_add_item_data($cart_item_data, $product_id, $variation_id)
{
    if($product_id == 65)
    {
      if (isset($_COOKIE['interior'])) {
        $cart_item_data['custom'] = "Interior: " + $_COOKIE["interior"];
      }
    }

    return $cart_item_data;
}

add_filter('woocommerce_get_item_data','custom_add_item_meta',10,2);
function custom_add_item_meta($item_data, $cart_item)
{
  if(array_key_exists('custom', $cart_item))
  {
    $custom_details = $cart_item['custom'];

    $item_data[] = array(
        'key'   => 'Details',
        'value' => $custom_details
    );
  }

  return $item_data;
}