JSFiddle - React, Tailwind, and code Playground

HTML

<span id="f000020">It is impossible to say how first the idea entered my brain;</span>

<span id="f000020t" onmouseover="highlighton('f000020', 'f000020t')" onmouseout="highlightoff('f000020', 'f000020t')">Es imposible decir cómo es que por vez primera la idea entró a mi cerebro;</span>

CSS

.highlight
{
    background-color: yellow;
}

JavaScript

function highlighton(id1, id2) {
    document.getElementById(id1).className += "highlight";
    document.getElementById(id2).className += "highlight";
}

function highlightoff(id1, id2) {
    document.getElementById(id1).className -= "highlight";
    document.getElementById(id2).className -= "highlight";
}