JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">
Blablabla
</div>

<div class="test" id="fit">
<span id="wrap">Blablabla12124e121211asdasasas</span>
</div>

CSS

.test {
  width: 200px;
  border: 1px solid black;
  font-size: 16px;
}

JavaScript

var fit = document.getElementById("fit"),
	wrap = document.getElementById("wrap"),
  step = 0.5,
  currentSize;

while (fit.offsetWidth < wrap.offsetWidth) {
  currentSize = parseFloat(window.getComputedStyle(wrap, null).getPropertyValue('font-size'));
	wrap.style.fontSize = (currentSize - step) + "px";
}