JSFiddle - React, Tailwind, and code Playground

HTML

<div class="class1">
 hello
</div>

CSS

.class1{
  background-color:red;
}

JavaScript

var color = $('.class1').css("background-color"); // this will return RGB() color even if it was html color before
var opacity = 0.5;
color = color.toString().replace(/\)/g,"," + opacity + ")");
$('.class1').css("background-color",color);