JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mybox"></div>
<div id="buttons">
    <input type="button" value="set" onclick="setColor('red')" />
    &nbsp;
    <input type="button" value="get" onclick="getColor()" />
</div>

CSS

#mybox {
    width: 100px;
    height: 100px;
    margin: auto;
    background-color: #eb5;
}
#buttons {
    text-align: center;
}

JavaScript

function getColor(color){
    var box = document.getElementById("mybox");
    alert(box.style.backgroundColor);
}
function setColor(color){
    var box = document.getElementById("mybox");
    box.style.backgroundColor = color;
}