JSFiddle - React, Tailwind, and code Playground

HTML

<span class="fraction">4/1</span>
<br>
<span class="fraction"><strike>4</strike>/1</span>

CSS

.top, .bottom {
  display: block;
}

.top {
  text-decoration: underline;
}

JavaScript

$('.fraction').each(function() {
  var split = $(this).text().split("/");
  if (split.length === 2) {
    $(this).html('<span class="top">' + split[0] + '</span><span class="bottom">' + split[1] + '</span>');
  }
});