JSFiddle - React, Tailwind, and code Playground
HTML
<div id='mydiv'>Lorem<span> ipsum</span> dolor amet</div>
CSS
.myClass {
background-color: yellow;
}
JavaScript
var elm = $('#mydiv');
highlite(elm, 2, 28);
function highlite(element, startpos, endpos) {
var rgxp = elm.html().substr(startpos,endpos)
var repl = '<span class="myClass">' + rgxp + '</span>';
elm.html(elm.html().replace(rgxp, repl));
}