diff --git a/package.json b/package.json
index 090ee18..bf32583 100644
--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
   "name": "@rolemodel/spider",
   "description": "Shared high level web components for RoleModel Software and beyond",
   "packageManager": "yarn@4.12.0",
-  "version": "0.0.9",
+  "version": "0.0.10",
   "author": "RoleModel Software",
   "license": "MIT",
   "type": "module",
diff --git a/src/components/pdf-viewer/pdf-viewer.js b/src/components/pdf-viewer/pdf-viewer.js
index dcaaddc..af32b8a 100644
--- a/src/components/pdf-viewer/pdf-viewer.js
+++ b/src/components/pdf-viewer/pdf-viewer.js
@@ -1,4 +1,4 @@
-import { html } from 'lit'
+import { html, adoptStyles } from 'lit'
 import { ContextProvider } from '@lit/context'
 import './url-parse-polyfill.js'
 import * as pdfjsLib from 'pdfjs-dist'
@@ -8,7 +8,7 @@ import openjpegWasmUrl from 'pdfjs-dist/wasm/openjpeg.wasm?url'
 import qcmsWasmUrl from 'pdfjs-dist/wasm/qcms_bg.wasm?url'
 import styles from './pdf-viewer.styles.js'
 import { pdfContext } from './pdf-context.js'
-import { createThemeStyleSheet } from './theme-config.js'
+import { createThemeStyles } from './theme-config.js'
 import { normalizeText } from './helpers/text-helper.js'
 import './toolbar/pdf-toolbar.js'
 import './sidebar/pdf-sidebar.js'
@@ -83,7 +83,7 @@ export default class PDFViewer extends RoleModelElement {
     this.searchOpen = false
     this.error = null
     this.loading = false
-    this.themeStyleSheet = createThemeStyleSheet(this.themeHue, this.themeSaturation)
+    this.themeStyleSheet = createThemeStyles(this.themeHue, this.themeSaturation)
     this.fitToScreenScale = null
 
     this._provider = new ContextProvider(this, {
@@ -381,11 +381,8 @@ export default class PDFViewer extends RoleModelElement {
   }
 
   _updateThemeColors() {
-    this.themeStyleSheet = createThemeStyleSheet(this.themeHue, this.themeSaturation)
-    this.shadowRoot.adoptedStyleSheets = [
-      ...this.constructor.elementStyles.map(s => s.styleSheet),
-      this.themeStyleSheet
-    ]
+    this.themeStyleSheet = createThemeStyles(this.themeHue, this.themeSaturation)
+    adoptStyles(this.shadowRoot, [...this.constructor.elementStyles, this.themeStyleSheet])
   }
 
   async firstUpdated() {
diff --git a/src/components/pdf-viewer/theme-config.js b/src/components/pdf-viewer/theme-config.js
index 6c339f1..df51c9e 100644
--- a/src/components/pdf-viewer/theme-config.js
+++ b/src/components/pdf-viewer/theme-config.js
@@ -1,5 +1,9 @@
-export const createThemeStyleSheet = (hue = 217, saturation = 89) => {
-  const css = `
+import { css } from 'lit'
+
+// Returns a lazy CSSResult instead of constructing a CSSStyleSheet directly:
+// `new CSSStyleSheet()` throws "Illegal constructor" on browsers without
+// constructable stylesheet support (e.g. Safari < 16.4).
+export const createThemeStyles = (hue = 217, saturation = 89) => css`
     :host {
       --theme-primary: light-dark(hsl(${hue}, ${saturation}%, 50%), hsl(${hue}, ${saturation}%, 60%));
       --theme-primary-light: light-dark(hsl(${hue}, ${saturation}%, 90%), hsl(${hue}, ${saturation}%, 30%));
@@ -44,8 +48,3 @@ export const createThemeStyleSheet = (hue = 217, saturation = 89) => {
       --theme-icon-size-lg: 18px;
     }
   `
-
-  const sheet = new CSSStyleSheet()
-  sheet.replaceSync(css)
-  return sheet
-}
diff --git a/test/components/theme-config.test.js b/test/components/theme-config.test.js
index d528304..9880637 100644
--- a/test/components/theme-config.test.js
+++ b/test/components/theme-config.test.js
@@ -1,32 +1,30 @@
 import { describe, it, expect } from 'vitest'
-import { createThemeStyleSheet } from '../../src/components/pdf-viewer/theme-config.js'
+import { CSSResult } from 'lit'
+import { createThemeStyles } from '../../src/components/pdf-viewer/theme-config.js'
 
 describe('Theme Configuration', () => {
-  describe('createThemeStyleSheet', () => {
-    it('should create a CSSStyleSheet with default values', () => {
-      const sheet = createThemeStyleSheet()
+  describe('createThemeStyles', () => {
+    it('should create a CSSResult with default values', () => {
+      const styles = createThemeStyles()
 
-      expect(sheet).toBeInstanceOf(CSSStyleSheet)
-      expect(sheet.cssRules.length).toBeGreaterThan(0)
+      expect(styles).toBeInstanceOf(CSSResult)
+      expect(styles.cssText.length).toBeGreaterThan(0)
     })
 
-    it('should create a stylesheet with custom hue', () => {
-      const sheet = createThemeStyleSheet(150, 89)
+    it('should create styles with custom hue', () => {
+      const styles = createThemeStyles(150, 89)
 
-      expect(sheet).toBeInstanceOf(CSSStyleSheet)
-      expect(sheet.cssRules[0].cssText).toContain('150')
+      expect(styles.cssText).toContain('150')
     })
 
-    it('should create a stylesheet with custom saturation', () => {
-      const sheet = createThemeStyleSheet(217, 50)
+    it('should create styles with custom saturation', () => {
+      const styles = createThemeStyles(217, 50)
 
-      expect(sheet).toBeInstanceOf(CSSStyleSheet)
-      expect(sheet.cssRules[0].cssText).toContain('50%')
+      expect(styles.cssText).toContain('50%')
     })
 
     it('should include all theme CSS variables', () => {
-      const sheet = createThemeStyleSheet()
-      const cssText = sheet.cssRules[0].cssText
+      const cssText = createThemeStyles().cssText
 
       expect(cssText).toContain('--theme-primary')
       expect(cssText).toContain('--theme-neutral-')
@@ -37,10 +35,22 @@ describe('Theme Configuration', () => {
     })
 
     it('should use light-dark() function for color properties', () => {
-      const sheet = createThemeStyleSheet()
-      const cssText = sheet.cssRules[0].cssText
+      const cssText = createThemeStyles().cssText
 
       expect(cssText).toContain('light-dark')
     })
+
+    it('should not construct a CSSStyleSheet eagerly (Safari < 16.4 has no constructor)', () => {
+      const originalCSSStyleSheet = globalThis.CSSStyleSheet
+      globalThis.CSSStyleSheet = function () {
+        throw new TypeError('Illegal constructor')
+      }
+
+      try {
+        expect(() => createThemeStyles(217, 89)).not.toThrow()
+      } finally {
+        globalThis.CSSStyleSheet = originalCSSStyleSheet
+      }
+    })
   })
 })