JSFiddle - React, Tailwind, and code Playground

HTML

<div class="widget_box">
    <div class="widget_box_content">
        <a href="#" class="widget_minimize">link</a>
        <div class="widget_box_content_cont">
            some content
        </div>
    </div>
</div>

JavaScript

var min = $(document.body).getElements('a.widget_minimize');
min.addEvent('click', function(event) {
    event.stop();
    //var box = ;
    var wid_cont = ($(this).getParents('.widget_box').getElement('.widget_box_content_cont'));
    console.log(wid_cont);
    var myVerticalSlide = new Fx.Slide(wid_cont[0]);
    myVerticalSlide.toggle();
});