index.js

const ModularScale = require('modularscale-js');

module.exports = function({
    sizes = [
        { size: 'sm', value: -1 },
        { size: 'base', value: 0 },
        { size: 'lg', value: 1 },
        { size: 'xl', value: 2 },
        { size: '2xl', value: 3 },
        { size: '3xl', value: 4 },
        { size: '4xl', value: 5 }
    ],
    base = 16,
    ratio = 1.33,
    unit = 'px',
    variants
}) {
    const ms = function(size) {
        const value = ModularScale(size, { base, ratio });

        if (unit === 'px') {
            return Math.round(value) + unit;
        } else {
            return value.toFixed(2) + unit;
        }
    }

    return function({ addUtilities }) {
        const utilities = sizes.map(({ size, value }) => ({
            [`.ms-${size}`]: {
                fontSize: ms(value),
            },
        }));

        addUtilities(utilities, variants);
    }
}