JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">
    <p>Some text</p>
    <img src="http://davidrhysthomas.co.uk/img/dexter.png" />
</div>

CSS

#test {
    background-color: rgba(0, 0, 0, 0);
    -webkit-transition:background-color 1s;
    -moz-transition:background-color 1s;
    transition:background-color 1s;
}

JavaScript

$('#test').css({ 'background-color': 'rgba(0, 0, 0, 0.7)' });