JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <h1>Elemento 1</h1><br/>
    <h1>Elemento 2</h1><br/>
    <h1 class='desactivado'>Elemento 3</h1><br/>
    <h1>Elemento 4</h1><br/>
    <h1>Elemento 5</h1><br/>
</body>

CSS

h1{
    background-color: black;
    color: white;
}
body {
    background-color: #DEACDE;
}

JavaScript

$('.desactivado').css('opacity', '0.3');