fix error when referencing a css file directly

src/index.js

@@ -36,6 +36,14 @@ module.exports = async (url, {waitUntil = 'networkidle0'} = {}) => {
 		)
 	}
 
+	// If the response is a CSS file, return that file
+	// instead of running our complicated setup
+	const headers = response.headers()
+
+	if (headers['content-type'].includes('text/css')) {
+		return Promise.resolve(response.text())
+	}
+
 	const coverage = await page.coverage.stopCSSCoverage()
 
 	// Get all CSS generated with the CSSStyleSheet API

test/index.js

@@ -84,6 +84,13 @@ test('it finds inline styles - JS', async t => {
 	t.snapshot(actual)
 })
 
+test('it returns a direct link to a CSS file', async t => {
+	const actual = await extractCss(server.url + '/import-in-css.css')
+
+	t.true(actual.includes('.css-imported-with-css {}'))
+	t.snapshot(actual)
+})
+
 test('it rejects if the url has an HTTP error status', async t => {
 	server.get('/404-page', (req, res) => {
 		res.status(404).send()

test/snapshots/index.js.md

@@ -78,3 +78,9 @@ Generated by [AVA](https://ava.li).
 
     `[x-extract-css-inline-style] { color: red; font-size: 12px; border-style: solid; }␊
     [x-extract-css-inline-style] { border-color: blue; border-width: 1px; }`
+
+## it returns a direct link to a CSS file
+
+> Snapshot 1
+
+    '.css-imported-with-css {}'