JSFiddle - React, Tailwind, and code Playground

HTML

<div style="width:200px; min-height:100px; background:#ccc;">
    <div class="Gray">
        this is Gray <br/>
        this is Gray <br/>
        this is Gray <br/>
        this is Gray <br/>
        this is Gray <br/>
        this is Gray <br/>
        this is Gray <br/>
        
    </div> 
    
    <div class="Blue">
        this is Blue <br/>
    </div> 
    
   <div style="clear:both; width:100%;"> 
</div>

CSS

.Gray{
    width:100px; min-height:200px; background:#333; float:left;
}

.Blue{
    width:50px;  background:#3b3ff5; float:left;
}

JavaScript

$('.Blue').height($('.Gray').height());
var gH = $(".Gray").height();
function checkResize(){
    var h = $(".Gray").height();
    if (h != gH) {    
        $('.Blue').height(h);
        gH = h;
    }
}
setInterval(checkResize, 1);
$('.Gray').click(function() {
    $('.Gray').height($('.Gray').height() + 10);
});