JSFiddle - React, Tailwind, and code Playground

HTML

<div id="t1">
    text1
</div>
<input name="reSize1" type="button" value="&nbsp;+&nbsp;" onclick="resizeText(1)" />
<input name="reSize2" type="button" value="&nbsp;-&nbsp;" onclick="resizeText(-1)" />


<div id="t2">
    text2
</div>
<input name="reSize3" type="button" value="&nbsp;+&nbsp;" onclick="resizeText(1)" />
<input name="reSize4" type="button" value="&nbsp;-&nbsp;" onclick="resizeText(-1)" />

JavaScript

function resizeText(multiplier) {
    var elem = document.getElementById("t1");
    var currentSize = elem.style.fontSize || 1;
    elem.style.fontSize = ( parseFloat(currentSize) + (multiplier * 0.2)) + "em";
}

function resizeText(multiplier) {
    var elem = document.getElementById("t2");
    var currentSize = elem.style.fontSize || 1;
    elem.style.fontSize = ( parseFloat(currentSize) + (multiplier * 0.2)) + "em";
}