JSFiddle - React, Tailwind, and code Playground

HTML

<div class='halfwidth'></div>

CSS

.halfwidth {
    width: 100%;
    height: 100px;
    background-color: #e0e0e0;
}

JavaScript

$(window).on( 'resize', function () {
    $('.halfwidth').height( $(window).width() / 2 );
}).resize();