JSFiddle - React, Tailwind, and code Playground

HTML

<input onclick="change()" type="button" value="Open Curtain" id="button1"></input>
<br>
    <span id="p2">Hidden text</span> Test for more 
    <span id="p2">Hidden text</span> test again. 
    <span id="p2">Hidden text</span>

CSS

.mask
{
color : red;
}

JavaScript

function change()
{
 var elements = document.getElementById("p2").parentNode.getElementsByTagName("span");
    for(var i=0; i<elements.length; i++)
      elements[i].className = "mask";
}