feat: allow disabling of default responsive image styles

.changeset/open-tables-sit.md

@@ -0,0 +1,22 @@
+---
+'astro': patch
+---
+
+Allows disabling default styles for responsive images
+
+This change adds a new `image.experimentalDefaultStyles` option that allows you to disable the default styles applied to responsive images. 
+
+When using experimental responsive images, Astro applies default styles to ensure the images resize correctly. In most cases this is what you want – and they are applied with low specificity so your own styles override them. However in some cases you may want to disable these default styles entirely. This is particularly useful when using Tailwind 4, because it uses CSS cascade layers to apply styles, making it difficult to override the default styles.
+
+`image.experimentalDefaultStyles` is a boolean option that defaults to `true`, so you can change it in your Astro config file like this:
+
+```js
+export default {
+  image: {
+    experimentalDefaultStyles: false,
+  },
+  experimental: {
+    responsiveImages: true,
+  },
+};
+```

packages/astro/src/assets/vite-plugin-assets.ts

@@ -109,7 +109,10 @@ export default function assets({ fs, settings, sync, logger }: Options): vite.Pl
 		referencedImages: new Set(),
 	};
 
-	const imageComponentPrefix = settings.config.experimental.responsiveImages ? 'Responsive' : '';
+	const imageComponentPrefix =
+		settings.config.experimental.responsiveImages && settings.config.image.experimentalDefaultStyles
+			? 'Responsive'
+			: '';
 	return [
 		// Expose the components and different utilities from `astro:assets`
 		{

packages/astro/src/core/config/schemas/base.ts

@@ -67,6 +67,7 @@ export const ASTRO_CONFIG_DEFAULTS = {
 	image: {
 		endpoint: { entrypoint: undefined, route: '/_image' },
 		service: { entrypoint: 'astro/assets/services/sharp', config: {} },
+		experimentalDefaultStyles: true,
 	},
 	devToolbar: {
 		enabled: true,
@@ -274,6 +275,9 @@ export const AstroConfigSchema = z.object({
 			experimentalObjectFit: z.string().optional(),
 			experimentalObjectPosition: z.string().optional(),
 			experimentalBreakpoints: z.array(z.number()).optional(),
+			experimentalDefaultStyles: z
+				.boolean()
+				.default(ASTRO_CONFIG_DEFAULTS.image.experimentalDefaultStyles),
 		})
 		.default(ASTRO_CONFIG_DEFAULTS.image),
 	devToolbar: z

packages/astro/src/types/public/config.ts

@@ -1367,6 +1367,16 @@ export interface ViteUserConfig extends OriginalViteUserConfig {
 		 * the more comprehensive list is used, because only the required sizes are generated. For local services, the list is shorter to reduce the number of images generated.
 		 */
 		experimentalBreakpoints?: number[];
+		/**
+		 * @docs
+		 * @name experimentalDefaultStyles
+		 * @type {boolean}
+		 * @default `true`
+		 * @description
+		 * Whether to automatically add global styles to ensure that experimental images resize correctly. This is enabled by default, but can be disabled if you want to manage the styles yourself.
+		 * This option is only used when the `experimental.responsiveImages` flag is enabled.
+		 */
+		experimentalDefaultStyles?: boolean;
 	};
 
 	/**

packages/astro/test/core-image-layout.test.js

@@ -584,7 +584,6 @@ describe('astro:image:layout', () => {
 
 			await fixture.build();
 		});
-
 		describe('basics', () => {
 			let $;
 			let html;
@@ -684,5 +683,22 @@ describe('astro:image:layout', () => {
 				assert.match(style, /\[data-astro-image\]/);
 			});
 		});
+		describe('disabling global styles', async () => {
+			it('allows disabling global styles', async () => {
+				const fixtureWithoutStyles = await loadFixture({
+					root: './fixtures/core-image-layout/',
+					image: {
+						service: testImageService({ foo: 'bar' }),
+						domains: ['avatars.githubusercontent.com'],
+						experimentalDefaultStyles: false,
+					},
+				});
+				await fixtureWithoutStyles.build();
+				const html = await fixtureWithoutStyles.readFile('/index.html');
+				const $ = cheerio.load(html);
+				const style = $('style').text();
+				assert.ok(!style.includes('[data-astro-image]'));
+			});
+		});
 	});
 });