JSFiddle - React, Tailwind, and code Playground

HTML

<div class="site-header">
  Element
</div>

CSS

.site-header {
  padding: 10px;
  border: 2px solid #f00;
  margin: 10px;
}

JavaScript

var elementHeight = document.querySelector('.site-header').offsetHeight;
var elementHeightjQuery = $('.site-header').outerHeight();

console.log(elementHeight);
console.log(elementHeightjQuery);