.parse(css) and then .stringify(theParsedObject) back into CSS

JSCN.js

// not ready for production, issues with pseudo selectors in nested rules parsing as props...
let JSCN = {

parse: function parse(str) { // css to object
	var sheet = {}, // holds all the selectors and rules
		rule = {}, // current rule
		float = "", // accumulates chars before determining what to do with them
		quoteMode = 0, // [none, single, double] quote mode
		sel = "",	// current selector
		prop = "",	// current property
		isInRule = false, // true when cursor between { and }
		heap = [sheet]; // for nested rules, [deep > shallow]

	function addPair() { // move prop:val pair to rule object
		if (prop) rule[prop] = float.trim();
		float = "";
		prop = "";
	}

	for (var i = 0; i < str.length; i++) { // parse char by char

		var it = str[i];

		if (it === '"') {
			if (str[i - 1] !== '\\') quoteMode = [2, 1, 0][quoteMode];
			float += '"';
			continue;
		} //end if "

		if (it === "'") {
			if (str[i - 1] !== '\\') quoteMode = [1, 0, 2][quoteMode];
			float += "'";
			continue;
		} //end if '

		if (it === ":") {
			if (!quoteMode && isInRule) {
				prop = float.trim();
				float = "";
			} else {
				float += ":";
			}
			continue;
		} //end if :

		if (it === ";") {
			if (!quoteMode) {
				addPair();
			} else {
				float += ";";
			}
			continue;
		} //end if ;

		if (it === "{") {
			if (!quoteMode) {
				sel = float.trim();
				float = "";

				rule =  heap.at(-1)[sel] || {};
				heap.at(-1)[sel] = rule;
				isInRule  = true;
				heap.push(rule);
				prop = "";
			} else {
				float += "{";
			}
			continue;
		} //end if {

		if (it === "}") {
			if (!quoteMode) {
				addPair();
				heap.pop();
				isInRule  = false;
				rule = heap.at(-1)[sel] || {};
				sel = "";
			} else {
				float += "}";
			}
			continue;
		} //end if }

		float += it;
	}

	addPair();
	return sheet;
}, //end parse()

stringify:   function stringify(objRules, blnCompress, _depth = 1) { // object to css
  	var [LINE, TAB, SPACE] = blnCompress ? ["", "", ""] : ["\n", "\t", " "];
  	return Object.entries(objRules).map(([sel, rule]) => {
  		return sel + SPACE + "{" + LINE + TAB.repeat(_depth) +
  			Object.entries(rule).map(([prop, val]) => {
  				if (typeof val === "object") return stringify({	[prop]: val}, blnCompress, _depth + 1);
  				return `${prop}:${SPACE}${val};`;
  			}).join(LINE + TAB.repeat(_depth)) +
  			LINE + TAB.repeat(_depth - 1) + "}";
  	}).join(LINE).trim();
  } // end stringify()
};// end JSCN