JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue/dist/vue.js"></script>

<div id="app">
	<div class="demo" @click="attachRed= !attachRed" :class="{red: attachRed}"></div>
	<div class="demo"></div>
	<div class="demo"></div>
</div>

CSS

.demo {
    width: 100px;
    height: 100px;
    background-color: gray;
    display: inline-block;
    margin: 10px;
}

.red {
    background-color: red;
}

.green {
    background-color: green;
}

.blue {
    background-color: blue;
}

JavaScript

new Vue({
    el: '#app',
    data: {
        attachRed: false
    }
})