@jlalmes/goober/src/core/astish.js

A less than 1KB css-in-js solution

let newRule = /(?:([\u0080-\uFFFF\w-%@]+) *:? *([^{;]+?);|([^;}{]*?) *{)|(})/g;
let ruleClean = /\/\*[^]*?\*\/|\s\s+|\n/g;

/**
 * Convert a css style string into a object
 * @param {String} val
 * @returns {Object}
 */
export let astish = (val) => {
    let tree = [{}];
    let block;

    while ((block = newRule.exec(val.replace(ruleClean, '')))) {
        // Remove the current entry
        if (block[4]) tree.shift();

        if (block[3]) {
            tree.unshift((tree[0][block[3]] = tree[0][block[3]] || {}));
        } else if (!block[4]) {
            tree[0][block[1]] = block[2];
        }
    }

    return tree[0];
};