JSFiddle - React, Tailwind, and code Playground

HTML

<div class="double_column_left">
    //Left responsive content
    If I add more content to this div then the other div will become the same height when the page loads.
</div>
<div class="double_column_right">
    //Right responsive content
</div>

CSS

.double_column_left{
    float:left;
    width:100px;
    background:#58c;
}
.double_column_right{
    float:left;
    width:100px;
    background:#333;
}

JavaScript

var col1 = $(".double_column_left").height(),
    col2 = $(".double_column_right").height();
if (col1 > col2) {$(".double_column_right").height(col1); } else {
    $(".double_column_left").height(col2);
}