JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
     <div style="background:green;"><button class="addContent">add content</button>content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content.
    </div>
    <div style="background:yellow;"><button class="addContent">add content</button>content content content content content content content content content content content content content content content content content content content content content content content content content content content content content content.
    </div>
</div>

CSS

.parent { display: table; }
.parent > div {display: table-cell; width:50%; }
/*omit width:50% for auto-scaled column widths*/
.child-left {background: yellow;}
.child-right {background: green;}

JavaScript

$('.addContent').click(
    function(el) {
        $(el.target.parentElement).append('  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam consequat quam bibendum nibh cursus viverra. Duis suscipit bibendum faucibus. Praesent sit amet lectus sapien, ut dignissim augue. Aliquam sollicitudin nisi a nunc lobortis mollis. Phasellus vitae dolor ac orci porttitor lacinia at at augue. In dui eros, sodales ac gravida at, adipiscing rhoncus dolor. In tellus purus, scelerisque eu suscipit venenatis, tincidunt sit amet risus. Nunc sed nibh eu neque mattis varius in eget erat. Etiam sit amet felis lacus, placerat tincidunt dolor. ');
    }
);