smaller-text.user.js

// ==UserScript==
// @name         Smashing smaller text.
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Smashing Magazine text size is ENORMOUS, so I try to make it more reasonable.
// @author       Josh Parker
// @match        https://www.smashingmagazine.com/*
// @icon         https://www.google.com/s2/favicons?domain=smashingmagazine.com
// @grant        none
// ==/UserScript==

(function smashingSmallerText() {
 // delete rules is meant to be reusable across many userscripts
 const deleteRules = (selector, ruleName) => {
  const styleSheets = [...document.styleSheets];
  styleSheets.forEach((styleSheet, ssi) => {
   const cssRules = [...styleSheet.cssRules];
   cssRules.forEach((cssRule, cri) => {
    const { cssText } = cssRule;
    const selectorRE = new RegExp(`${selector}.*\\{`, 'i');
    if (cssText.match(selectorRE)) {
     const rulesRE = /\{(.*)\}/;
     const rulesText = cssText.match(rulesRE)[1].trim();
     const ruleRE = /[^;]*;/g;
     const rules = rulesText.match(ruleRE);
     rules.forEach((rule) => {
      const ruleNameRE = new RegExp(`^${ruleName}:`, 'i');
      if (rule.match(ruleNameRE)) {
       document.styleSheets[ssi].deleteRule(cri);
      }
     });
    }
   });
  });
 };

 deleteRules('body', 'font-size');
 document.styleSheets[0].insertRule('body { font-size: 15px; }');
}());