diff --git a/.changeset/poor-frogs-melt.md b/.changeset/poor-frogs-melt.md
new file mode 100644
index 000000000..a07930d29
--- /dev/null
+++ b/.changeset/poor-frogs-melt.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix CSS styles on Windows
diff --git a/packages/astro/src/content/vite-plugin-content-assets.ts b/packages/astro/src/content/vite-plugin-content-assets.ts
index 5d82a684f..133fc9edd 100644
--- a/packages/astro/src/content/vite-plugin-content-assets.ts
+++ b/packages/astro/src/content/vite-plugin-content-assets.ts
@@ -64,7 +64,7 @@ export function astroContentAssetPropagationPlugin({
 					if (!devModuleLoader.getModuleById(basePath)?.ssrModule) {
 						await devModuleLoader.import(basePath);
 					}
-					const { stylesMap, urls } = await getStylesForURL(
+					const { styles, urls } = await getStylesForURL(
 						pathToFileURL(basePath),
 						devModuleLoader,
 						'development'
@@ -77,7 +77,7 @@ export function astroContentAssetPropagationPlugin({
 					);
 
 					stringifiedLinks = JSON.stringify([...urls]);
-					stringifiedStyles = JSON.stringify([...stylesMap.values()]);
+					stringifiedStyles = JSON.stringify(styles.map((s) => s.content));
 					stringifiedScripts = JSON.stringify([...hoistedScripts]);
 				} else {
 					// Otherwise, use placeholders to inject styles and scripts
diff --git a/packages/astro/src/vite-plugin-astro-server/css.ts b/packages/astro/src/vite-plugin-astro-server/css.ts
index d256f48c7..0da51db1e 100644
--- a/packages/astro/src/vite-plugin-astro-server/css.ts
+++ b/packages/astro/src/vite-plugin-astro-server/css.ts
@@ -4,14 +4,21 @@ import { viteID } from '../core/util.js';
 import { isBuildableCSSRequest } from './util.js';
 import { crawlGraph } from './vite.js';
 
+interface ImportedStyle {
+	id: string;
+	url: string;
+	content: string;
+}
+
 /** Given a filePath URL, crawl Vite’s module graph to find all style imports. */
 export async function getStylesForURL(
 	filePath: URL,
 	loader: ModuleLoader,
 	mode: RuntimeMode
-): Promise<{ urls: Set<string>; stylesMap: Map<string, string> }> {
+): Promise<{ urls: Set<string>; styles: ImportedStyle[] }> {
 	const importedCssUrls = new Set<string>();
-	const importedStylesMap = new Map<string, string>();
+	// Map of url to injected style object. Use a `url` key to deduplicate styles
+	const importedStylesMap = new Map<string, ImportedStyle>();
 
 	for await (const importedModule of crawlGraph(loader, viteID(filePath), true)) {
 		if (isBuildableCSSRequest(importedModule.url)) {
@@ -28,7 +35,11 @@ export async function getStylesForURL(
 				mode === 'development' && // only inline in development
 				typeof ssrModule?.default === 'string' // ignore JS module styles
 			) {
-				importedStylesMap.set(importedModule.id ?? importedModule.url, ssrModule.default);
+				importedStylesMap.set(importedModule.url, {
+					id: importedModule.id ?? importedModule.url,
+					url: importedModule.url,
+					content: ssrModule.default,
+				});
 			} else {
 				// NOTE: We use the `url` property here. `id` would break Windows.
 				importedCssUrls.add(importedModule.url);
@@ -38,6 +49,6 @@ export async function getStylesForURL(
 
 	return {
 		urls: importedCssUrls,
-		stylesMap: importedStylesMap,
+		styles: [...importedStylesMap.values()],
 	};
 }
diff --git a/packages/astro/src/vite-plugin-astro-server/route.ts b/packages/astro/src/vite-plugin-astro-server/route.ts
index 34ab119da..069c2ffe8 100644
--- a/packages/astro/src/vite-plugin-astro-server/route.ts
+++ b/packages/astro/src/vite-plugin-astro-server/route.ts
@@ -293,7 +293,11 @@ async function getScriptsAndStyles({ pipeline, filePath }: GetScriptsAndStylesPa
 	}
 
 	// Pass framework CSS in as style tags to be appended to the page.
-	const { urls: styleUrls, stylesMap } = await getStylesForURL(filePath, moduleLoader, mode);
+	const { urls: styleUrls, styles: importedStyles } = await getStylesForURL(
+		filePath,
+		moduleLoader,
+		mode
+	);
 	let links = new Set<SSRElement>();
 	[...styleUrls].forEach((href) => {
 		links.add({
@@ -306,7 +310,7 @@ async function getScriptsAndStyles({ pipeline, filePath }: GetScriptsAndStylesPa
 	});
 
 	let styles = new Set<SSRElement>();
-	[...stylesMap].forEach(([url, content]) => {
+	importedStyles.forEach(({ id, url, content }) => {
 		// Vite handles HMR for styles injected as scripts
 		scripts.add({
 			props: {
@@ -319,7 +323,7 @@ async function getScriptsAndStyles({ pipeline, filePath }: GetScriptsAndStylesPa
 		// should emulate what Vite injects so further HMR works as expected.
 		styles.add({
 			props: {
-				'data-vite-dev-id': url,
+				'data-vite-dev-id': id,
 			},
 			children: content,
 		});