JSFiddle - React, Tailwind, and code Playground

HTML

<div class='parent'>
    <div>Foo</div>
    <div>Foo</div>
    <div>Foo</div>
    <div>Foo</div>
    <div>Foo</div>
</div>

CSS

@define { multiplier: 10; }
.parent {counter-reset: num;}
.parent div {
    counter-increment: num;
    font-size: -moz-calc( num* 10px);
}