KeepFixedWidth.tamper.js

// ==UserScript==
// @name         KeepFixedWidth
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  use fixed width for google keep
// @author       You
// @match        https://keep.google.com/
// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

function GM_addStyle(css) {
  const style = document.getElementById("GM_addStyleBy8626") || (function() {
    const style = document.createElement('style');
    style.type = 'text/css';
    style.id = "GM_addStyleBy8626";
    document.head.appendChild(style);
    return style;
  })();
  const sheet = style.sheet;
  sheet.insertRule(css, (sheet.rules || sheet.cssRules || []).length);
}

    // Your code here...
    GM_addStyle('div[role="textbox"]{font-family: D2Coding, "D2 coding", fixed !important;}');
})();