JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cdn.ractivejs.org/edge/ractive.js"></script>
<script id='template' type='text/ractive'>
    <p class="{{class}}">Hohoho</p>
    
    <button onclick="data.class = 'blue'; window.alert(data.class);">Make it blue</button>
</script>

CSS

.red {
    color: red;
}

.blue {
    color: blue;
}

JavaScript

var data = {
    class: ''
}
var ractive = new Ractive({
    el: document.body,
    template: '#template',
    magic: true,
    data: data
});

data.class = 'red'