JSFiddle - React, Tailwind, and code Playground

HTML

<div><h1>red</h1></div>

<div foo="blue">
    <h1>blue</h1>
</div>

<div foo="green">
    <h1>green</h1>
</div>

CSS

h1 {
    background-color:red;
}

[foo="blue"] h1 {
    background-color:blue;
}

* + [foo="green"] h1 {
    background-color:green;
}