JSFiddle - React, Tailwind, and code Playground

HTML

<div class = "label_wrapper">
    <label for = "two">Заголовок</label>
  </div>
  <div class = "checkbox_wrapper">
    <input type = "checkbox" id = "two" name = "two">
  </div>

CSS

label {font-size: 15px;}
label.big {font-size: 50px;}

JavaScript

$('input').click(function(event) {
    var method = this.checked ? 'addClass' : 'removeClass',
        className = 'big';
    $('label')[method](className);
    
});