JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#" onclick="changeText(125)">bigger</a>

<a href="#" onclick="changeText(100)">normal</a>

<a href="#" onclick="changeText(75)">smaller</a>

JavaScript

function changeText(size) {
    var obj = document.getElementsByTagName('html')[0];
    obj.style.fontSize = size + '%';
}