JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <label class="fine">
        <span>LABEL NAME |</span>
        <strong>ERROR MESSAGE</strong><!--innerHTML changed by JS-->
    </label>
</form>

CSS

form label.fine{
    display: block; 
    position: relative;
    background-color: #212121;
    color: #fff;
    font-size: 0.8em;
    padding:0.5em 0.5em;
    border-bottom:1px solid #ff2222; 
    border-radius:0.2em 0.2em 0.2em 0.2em;
    
}

form label.fine span,
form label.fine strong 
{
    display: inline-block; 
    vertical-align: baseline;
}

form label.fine strong
{
    font-size: 0.6em;
    color:#ff2222; //changed by JS
    text-decoration:bold;
}