JSFiddle - React, Tailwind, and code Playground

HTML

<div class="redBG">
    <div class="yellowIcon"></div>
</div>   
<div class="greenBG">
    <div class="yellowIcon"></div>
</div>

CSS

.redBG{
    background-color:red;
    width: 300px;
    height:30px;
    z-index: 1;
}
.grayBG{
    background-color: gray;
}
.yellowIcon{
    background-color:yellow;
    width: 20px;
    height:20px;
    cursor: pointer;
    z-index:20;
}
.greenBG{background-color:green}

.black{background-color:black}

JavaScript

$('div, .redBG').load(
    function()
    {
        $(this).removeClass('.redBG').addClass('.black');
    }
);