JSFiddle - React, Tailwind, and code Playground

HTML

<button id="red">Red</button>
<button id="blue">Blue</button>
<div id="square"></div>

CSS

#square {
    width: 100px;
    height: 100px;
}

#square[data-color=red] {
    background-color: red;
}

#square[data-color=blue] {
    background-color: blue;
}

JavaScript

red.addEventListener("click", function() {
    square.dataset.color="red";
});

blue.addEventListener("click", function() {
    square.dataset.color="blue";
});