expressive-code · matthewp · Aug 11, 2026 · Aug 11, 2026
diff --git a/packages/@expressive-code/core/package.json b/packages/@expressive-code/core/package.json
@@ -45,12 +45,10 @@
   },
   "dependencies": {
     "@ctrl/tinycolor": "^4.0.4",
-    "hast-util-select": "^6.0.2",
+    "@eslint/css-tree": "3.6.9",
     "hast-util-to-html": "^9.0.1",
     "hast-util-to-text": "^4.0.1",
     "hastscript": "^9.0.0",
-    "postcss": "^8.4.38",
-    "postcss-nested": "^6.0.1",
     "unist-util-visit": "^5.0.0",
     "unist-util-visit-parents": "^6.0.1"
   },
@@ -59,6 +57,7 @@
     "@types/hast": "^3.0.4",
     "culori": "^4.0.1",
     "djb2a": "^2.0.0",
+    "hast-util-select": "^6.0.2",
     "hast-util-sanitize": "^5.0.1",
     "shiki": "^4.0.2",
     "strip-json-comments": "^5.0.1"

diff --git a/packages/@expressive-code/core/src/common/engine.ts b/packages/@expressive-code/core/src/common/engine.ts
@@ -352,7 +352,7 @@ export class ExpressiveCodeEngine implements ResolvedExpressiveCodeEngineConfig
 			})
 		}
 		// Process styles (scoping, minifying, etc.)
-		const processedStyles = await processPluginStyles(pluginStyles)
+		const processedStyles = processPluginStyles(pluginStyles)
 		return wrapInCascadeLayer([...processedStyles].join(''), this.cascadeLayer)
 	}
 
@@ -376,6 +376,8 @@ export class ExpressiveCodeEngine implements ResolvedExpressiveCodeEngineConfig
 	 * Please note that these styles must be added to the page together with the base styles
 	 * returned by {@link getBaseStyles}.
 	 */
+	// Keep the public Promise-returning API even though CSS processing is synchronous.
+	// eslint-disable-next-line @typescript-eslint/require-await
 	async getThemeStyles(): Promise<string> {
 		const themeStyles: string[] = []
 		const renderDeclarations = (declarations: Map<string, string>) => [...declarations].map(([varName, varValue]) => `${varName}:${varValue}`).join(';')
@@ -404,7 +406,7 @@ export class ExpressiveCodeEngine implements ResolvedExpressiveCodeEngineConfig
 			.filter((selector) => selector)
 			.join(',')
 		themeStyles.push(
-			await scopeAndMinifyNestedCss(`
+			scopeAndMinifyNestedCss(`
 				${baseVarSelectors} {
 					${renderDeclarations(baseVars)}
 				}
@@ -448,7 +450,7 @@ export class ExpressiveCodeEngine implements ResolvedExpressiveCodeEngineConfig
 						this.themes.map((theme) => `${theme.name} (${theme.type})`).join(', '),
 					].join(' ')
 				)
-			const darkModeMediaQuery = await scopeAndMinifyNestedCss(`
+			const darkModeMediaQuery = scopeAndMinifyNestedCss(`
 				@media (prefers-color-scheme: ${altType}) {
 					${this.themeCssRoot}${notBaseThemeSelector} {
 						${firstAltVariant.cssVars}
@@ -468,7 +470,7 @@ export class ExpressiveCodeEngine implements ResolvedExpressiveCodeEngineConfig
 				if (!themeSelector) continue
 
 				themeStyles.push(
-					await scopeAndMinifyNestedCss(`
+					scopeAndMinifyNestedCss(`
 						${this.themeCssRoot}${themeSelector} &${notBaseThemeSelector}, &${themeSelector} {
 							${cssVars};
 							${coreStyles}

diff --git a/packages/@expressive-code/core/src/hast.ts b/packages/@expressive-code/core/src/hast.ts
@@ -5,8 +5,10 @@ import { matches, select, selectAll } from 'hast-util-select'
 import { visit } from 'unist-util-visit'
 import { visitParents, CONTINUE, EXIT, SKIP } from 'unist-util-visit-parents'
 import { h, s } from 'hastscript'
-import postcss, { Declaration } from 'postcss'
+import type { DeclarationList } from '@eslint/css-tree'
+import { generate, parse } from './internal/css-tree'
 import { serializeCssStringValue } from './internal/escaping'
+import { validateCssDelimiters } from './internal/css'
 
 export { visit, visitParents, CONTINUE, EXIT, SKIP }
 export { toHtml, toText, matches, select, selectAll, h, s }
@@ -72,19 +74,23 @@ export function getInlineStyles(node: Element): Map<string, string> {
 	const styleString = node.properties?.style?.toString().trim() || ''
 	if (!styleString) return styles
 
-	// @ts-expect-error PostCSS has incorrect types when using exactOptionalPropertyTypes
-	const postCssOptions: { from?: string } = { from: undefined }
-
-	// Attempt to parse the style string and extract its root-level declarations
 	try {
-		const root = postcss.parse(styleString, postCssOptions)
-
-		// Extract all root-level declarations into the styles map
-		root.each((node) => {
-			if (node.type === 'decl') styles.set(node.prop, node.value)
-		})
+		validateCssDelimiters(styleString)
+		const declarationList = parse(styleString, {
+			context: 'declarationList',
+			positions: true,
+			onParseError(error) {
+				throw error
+			},
+		}) as DeclarationList
+		for (const declaration of declarationList.children) {
+			if (declaration.type !== 'Declaration') throw new Error('Invalid inline style declaration')
+			const value = declaration.value.loc ? styleString.slice(declaration.value.loc.start.offset, declaration.value.loc.end.offset).trim() : generate(declaration.value)
+			styles.set(declaration.property, value)
+		}
 	} catch {
 		// Treat invalid inline styles as if they were empty
+		styles.clear()
 	}
 
 	return styles
@@ -96,17 +102,7 @@ export function getInlineStyles(node: Element): Map<string, string> {
  * Any existing styles will be overwritten.
  */
 export function setInlineStyles(node: Element, styles: Map<string, string>) {
-	const styleString = [...styles]
-		.map(([prop, value]) =>
-			new Declaration({
-				prop,
-				value,
-				raws: {
-					between: ':',
-				},
-			}).toString()
-		)
-		.join(';')
+	const styleString = [...styles].map(([prop, value]) => `${prop}:${value}`).join(';')
 	setProperty(node, 'style', styleString)
 }
 

diff --git a/packages/@expressive-code/core/src/internal/css-tree.ts b/packages/@expressive-code/core/src/internal/css-tree.ts
@@ -0,0 +1,7 @@
+import type * as CssTree from '@eslint/css-tree'
+// @ts-expect-error The browser bundle is exported without a matching declaration file.
+import * as browserRuntime from '@eslint/css-tree/dist/csstree.esm'
+
+const cssTree = browserRuntime as Pick<typeof CssTree, 'fork' | 'generate' | 'parse' | 'walk'>
+
+export const { fork, generate, parse, walk } = cssTree