JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="grid-6 push-3 equal" style="height: 999px;">
        <div class="block">
            <div id="mainbody"> 
                <!-- Body content here --> 
            </div>
        </div>
    </div>

    <div class="grid-2 equal">
        <div class="block">
            <div id="sidebar-a"> 
              sdfdsfsdfdsffsdfsdf
            </div>
        </div>
    </div>

    <div class="grid-2 equal" style="height: 999px;">
        <div class="block">
            <div id="sidebar-b"> 
                <!-- Sidebar-b content here --> 
            </div>
        </div>
    </div>

    <div class="grid-2 equal" style="height: 999px;">
        <div class="block">
            <div id="sidebar-c"> 
                <!-- Sidebar-c content here --> 
            </div>
        </div>
    </div>
</div>

JavaScript

$('div.equal div.block div[id^="sidebar-a"]').each(function() {
    $(this).closest('div.equal').addClass(this.id);
});