amazon_invoice_compressor.user.js

// ==UserScript==
// @name         Amazon invoice compressor
// @namespace    https://dacer.im/
// @version      0.1
// @description  Remove amazon invoice page's custom font
// @author       Dacer
// @grant        none
// @match        https://www.amazon.co.jp/gp/css/summary/print.html/*
// ==/UserScript==

// USAGE:
// 1. Install https://violentmonkey.github.io/get-it/
// 2. Click the 'Raw' in this page (at the top-right corner ↗)
// 3. Click the 'Confirm Installation' in the popup window
// DONE!

(function() {
    'use strict';
    var sheet = window.document.styleSheets[0];
    sheet.insertRule('* {font-family: Arial !important;}', sheet.cssRules.length);
})();