JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td>T1</td>
        <td>T2</td>
        <td>T3</td>
    </tr>
    <tr>
        <td>t4</td>
        <td>t5</td>
        <td>t6</td>
    </tr>
</table>
<input type="button" value="Decrease" onclick="decreaseFontSize();">
    <input type="button" value="Increase" onclick="increaseFontSize();">

JavaScript

var min=10;
var max=18;
function increaseFontSize() {

   var p = document.getElementsByTagName('td');
   for(i=0;i<p.length;i++) {

       p[i].style.fontSize = max+"px"

   }
}

function decreaseFontSize() {

   var p = document.getElementsByTagName('td');
   for(i=0;i<p.length;i++) {
      p[i].style.fontSize = min+"px"

   }
}