JSFiddle - React, Tailwind, and code Playground

HTML

<label for="some-box">Check me!</label>
<input type="checkbox" checked="checked" id="some-box" />

<div id="main-box" style="width:300px;height:300px;background:#ccc; display:none;"></div>

JavaScript

(function(d, $) {
    var $somebox = $('#some-box'),
        $mainbox = $('#main-box');
    
    var toggleMain = function() {
        $mainbox.slideToggle();
    };
    if($somebox.is(':checked')) {
        toggleMain();
    }
    $somebox.on('click', toggleMain);
})(document, jQuery);