JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">3</div>
<div class="test">7</div>
<div class="test">10</div>
<div class="test">23</div>

CSS

.red {
  color: red;
}

JavaScript

const elements = document.getElementsByClassName('test');

function elementsValueCheck() {

  for (var i = 0, length = elements.length; i < length; ++i) {

    if (Number(elements[i].textContent) < 10) {
      elements[i].classList.add('red');
    } else {
      elements[i].classList.remove('red');
    }

  }

}

elementsValueCheck();