countCssRules.js

[document, ...Array.from(document.querySelectorAll('iframe'), frame => frame.contentDocument)]
	.flatMap(doc => Array.from(doc.styleSheets))
	.flatMap(sheet => Array.from(sheet.cssRules))
	.flatMap(rule => {
		if (!rule) return [];
		if (rule.type === 1) return rule;
		if (rule.type === 4 || rule.type === 12) return Array.from(rule.cssRules);
		return [];
	}).length;

// Counts CSS rules in document, excluding @import, nested frames, CSS in JS, and inline CSS
// not working in Firefox console due to restrictions with document.styleSheets
// shamelessly lifted from https://twitter.com/sir_pepe/status/1296821191219478534