Fix CSS ordering between imported and Astro styles (#4907)

* Fix CSS ordering between imported and Astro styles

* Fix linting errors

* Add changeset and upgrade compiler version

* Update test to reflect shared styles placed before page styles

12 files changed, 218 insertions, 7 deletions

diff --git a/.changeset/small-bugs-prove.md b/.changeset/small-bugs-prove.md
new file mode 100644
index 000000000..16a89271d
--- /dev/null
+++ b/.changeset/small-bugs-prove.md
@@ -0,0 +1,34 @@
+---
+'astro': minor
+---
+
+Order Astro styles last, to override imported styles
+
+This fixes CSS ordering so that imported styles are placed *higher* than page/component level styles. This means that if you do:
+
+```astro
+---
+import '../styles/global.css';
+---
+<style>
+  body {
+    background: limegreen;
+  }
+</style>
+```
+
+The `<style>` defined in this component will be placed *below* the imported CSS. When compiled for production this will result in something like this:
+
+```css
+/* /src/styles/global.css */
+body {
+  background: blue;
+}
+
+/* /src/pages/index.astro */
+body:where(.astro-12345) {
+  background: limegreen;
+}
+```
+
+Given Astro's 0-specificity hashing, this change effectively makes it so that Astro styles "win" when they have the same specificity as global styles.
diff --git a/packages/astro/package.json b/packages/astro/package.json
index 0a39c75e1..de6483e9d 100644
--- a/packages/astro/package.json
+++ b/packages/astro/package.json
@@ -95,7 +95,7 @@
     "test:e2e:match": "playwright test -g"
   },
   "dependencies": {
-    "@astrojs/compiler": "^0.24.0",
+    "@astrojs/compiler": "^0.25.0",
     "@astrojs/language-server": "^0.26.2",
     "@astrojs/markdown-remark": "^1.1.2",
     "@astrojs/telemetry": "^1.0.0",
diff --git a/packages/astro/test/css-order-import.test.js b/packages/astro/test/css-order-import.test.js
new file mode 100644
index 000000000..91cecadab
--- /dev/null
+++ b/packages/astro/test/css-order-import.test.js
@@ -0,0 +1,114 @@
+import { expect } from 'chai';
+import * as cheerio from 'cheerio';
+import { loadFixture } from './test-utils.js';
+
+describe('CSS ordering - import order', () => {
+	/** @type {import('./test-utils').Fixture} */
+	let fixture;
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/css-order-import/',
+		});
+	});
+
+	/**
+	 * 
+	 * @param {string} html 
+	 * @returns {string[]}
+	 */
+	function getLinks(html) {
+		let $ = cheerio.load(html);
+		let out = [];
+		$('link[rel=stylesheet]').each((i, el) => {
+			out.push($(el).attr('href'));
+		});
+		return out;
+	}
+
+	function getStyles(html) {
+		let $ = cheerio.load(html);
+		let out = [];
+		$('style').each((i, el) => {
+			out.push($(el).text());
+		});
+		return out;
+	}
+
+	/**
+	 *
+	 * @param {string} href
+	 * @returns {Promise<{ href: string; css: string; }>}
+	 */
+	async function getLinkContent(href) {
+		const css = await fixture.readFile(href);
+		return { href, css };
+	}
+
+	describe('Development', () => {
+		/** @type {import('./test-utils').DevServer} */
+		let devServer;
+
+		before(async () => {
+			devServer = await fixture.startDevServer();
+		});
+
+		after(async () => {
+			await devServer.stop();
+		});
+
+		it('Page level CSS is defined lower in the page', async () => {
+			let res = await fixture.fetch('/');
+			let html = await res.text();
+			let [style1, style2] = getStyles(html);
+
+			expect(style1).to.include('green');
+			expect(style2).to.include('salmon');
+		});
+
+		it('import order is depth-first', async () => {
+			let res = await fixture.fetch('/component/');
+			let html = await res.text();
+			let [style1, style2, style3] = getStyles(html);
+
+			expect(style1).to.include('burlywood');
+			expect(style2).to.include('aliceblue');
+			expect(style3).to.include('whitesmoke');
+		});
+	});
+
+	describe('Production', () => {
+		before(async () => {
+			await fixture.build();
+		});
+
+		it('Page level CSS is defined lower in the page', async () => {
+			let html = await fixture.readFile('/index.html');
+
+			const content = await Promise.all(
+				getLinks(html).map((href) => getLinkContent(href))
+			);
+
+			const [{ css }] = content;
+			let idx1 = css.indexOf('salmon');
+			let idx2 = css.indexOf('green');
+
+			expect(idx1).to.be.greaterThan(idx2, 'Page level CSS should be placed after imported CSS');
+		});
+
+		it('import order is depth-first', async () => {
+			let html = await fixture.readFile('/component/index.html');
+
+			const content = await Promise.all(
+				getLinks(html).map((href) => getLinkContent(href))
+			);
+
+			const [{ css }] = content;
+			let idx1 = css.indexOf('whitesmoke');
+			let idx2 = css.indexOf('aliceblue');
+			let idx3 = css.indexOf('burlywood');
+
+			expect(idx1).to.be.greaterThan(idx2);
+			expect(idx2).to.be.greaterThan(idx3);
+		});
+	});
+});
diff --git a/packages/astro/test/css-order.test.js b/packages/astro/test/css-order.test.js
index fbcd580dd..e3333b875 100644
--- a/packages/astro/test/css-order.test.js
+++ b/packages/astro/test/css-order.test.js
@@ -87,9 +87,10 @@ describe('CSS production ordering', () => {
 			);
 
 			expect(content).to.have.a.lengthOf(3, 'there are 3 stylesheets');
-			const [, found] = content;
+			const [, sharedStyles, pageStyles] = content;
 
-			expect(found.css).to.match(/#00f/);
+			expect(sharedStyles.css).to.match(/red/);
+			expect(pageStyles.css).to.match(/#00f/);
 		});
 
 		it('CSS injected by injectScript comes first because of import order', async () => {
diff --git a/packages/astro/test/fixtures/css-order-import/package.json b/packages/astro/test/fixtures/css-order-import/package.json
new file mode 100644
index 000000000..2901a838f
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "@test/css-order-import",
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/css-order-import/src/components/One.astro b/packages/astro/test/fixtures/css-order-import/src/components/One.astro
new file mode 100644
index 000000000..54b1039b1
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/components/One.astro
@@ -0,0 +1,4 @@
+---
+import '../styles/One.css';
+---
+<link>
diff --git a/packages/astro/test/fixtures/css-order-import/src/components/Two.astro b/packages/astro/test/fixtures/css-order-import/src/components/Two.astro
new file mode 100644
index 000000000..1afb0ef87
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/components/Two.astro
@@ -0,0 +1,5 @@
+<style>
+	body {
+		background: aliceblue;
+	}
+</style>
diff --git a/packages/astro/test/fixtures/css-order-import/src/pages/component.astro b/packages/astro/test/fixtures/css-order-import/src/pages/component.astro
new file mode 100644
index 000000000..018ab1866
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/pages/component.astro
@@ -0,0 +1,19 @@
+---
+import One from '../components/One.astro';
+import Two from '../components/Two.astro';
+---
+<html>
+<head>
+	<title>Test</title>
+	<One />
+	<Two />
+	<style>
+		body {
+			background: whitesmoke;
+		}
+	</style>
+</head>
+<body>
+	<h1>Test</h1>
+</body>
+</html>
diff --git a/packages/astro/test/fixtures/css-order-import/src/pages/index.astro b/packages/astro/test/fixtures/css-order-import/src/pages/index.astro
new file mode 100644
index 000000000..0843250c0
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/pages/index.astro
@@ -0,0 +1,16 @@
+---
+import '../styles/base.css';
+---
+<html>
+<head>
+	<title>Test</title>
+	<style>
+		body {
+			background: salmon;
+		}
+	</style>
+</head>
+<body>
+	<h1>Test</h1>
+</body>
+</html>
diff --git a/packages/astro/test/fixtures/css-order-import/src/styles/One.css b/packages/astro/test/fixtures/css-order-import/src/styles/One.css
new file mode 100644
index 000000000..66d2bb71b
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/styles/One.css
@@ -0,0 +1,3 @@
+body {
+	background: burlywood;
+}
diff --git a/packages/astro/test/fixtures/css-order-import/src/styles/base.css b/packages/astro/test/fixtures/css-order-import/src/styles/base.css
new file mode 100644
index 000000000..828bff206
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order-import/src/styles/base.css
@@ -0,0 +1,3 @@
+body {
+	background: green;
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index aaeec592c..67b08ecc1 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -349,7 +349,7 @@ importers:
 
   packages/astro:
     specifiers:
-      '@astrojs/compiler': ^0.24.0
+      '@astrojs/compiler': ^0.25.0
       '@astrojs/language-server': ^0.26.2
       '@astrojs/markdown-remark': ^1.1.2
       '@astrojs/telemetry': ^1.0.0
@@ -443,7 +443,7 @@ importers:
       yargs-parser: ^21.0.1
       zod: ^3.17.3
     dependencies:
-      '@astrojs/compiler': 0.24.0
+      '@astrojs/compiler': 0.25.0
       '@astrojs/language-server': 0.26.2
       '@astrojs/markdown-remark': link:../markdown/remark
       '@astrojs/telemetry': link:../telemetry
@@ -1584,6 +1584,12 @@ importers:
     dependencies:
       astro: link:../../..
 
+  packages/astro/test/fixtures/css-order-import:
+    specifiers:
+      astro: workspace:*
+    dependencies:
+      astro: link:../../..
+
   packages/astro/test/fixtures/custom-404:
     specifiers:
       astro: workspace:*
@@ -3639,8 +3645,8 @@ packages:
     resolution: {integrity: sha512-vBMPy9ok4iLapSyCCT1qsZ9dK7LkVFl9mObtLEmWiec9myGHS9h2kQY2xzPeFNJiWXUf9O6tSyQpQTy5As/p3g==}
     dev: false
 
-  /@astrojs/compiler/0.24.0:
-    resolution: {integrity: sha512-xZ81C/oMfExdF18I1Tyd2BKKzBqO+qYYctSy4iCwH4UWSo/4Y8A8MAzV1hG67uuE7hFRourSl6H5KUbhyChv/A==}
+  /@astrojs/compiler/0.25.0:
+    resolution: {integrity: sha512-thJdIFuKT7f6uzxUs5d7qjh3g/L4kmlSfddAcbC62QEMy4H9N9fig3+FBwg9exUvXYcqOjZ/nC2PsGsVIqmZYA==}
     dev: false
 
   /@astrojs/language-server/0.26.2: