JSFiddle - React, Tailwind, and code Playground

HTML

<div id="square">
hi
</div>
<script>
    var a=document.getElementById('square');
    a.style.height=a.offsetWidth+'px';
    

</script>

CSS

#square {
    display: block;
    width: 50%;
    background: black;
}

JavaScript

window.onresize=function resizeit(){
    var a=document.getElementById('square');
    a.style.height=a.offsetWidth+'px';
};