diff --git a/books.html b/books.html
index bfa2e6e..d4e281c 100644
--- a/books.html
+++ b/books.html
@@ -47,23 +47,8 @@
             font-size: 0.9rem;
         }
     </style>
+    <script src="js/theme.js"></script>
     <script>
-        // Check for saved theme preference or default to light mode
-        const currentTheme = localStorage.getItem('theme') || 'light';
-        document.documentElement.setAttribute('data-theme', currentTheme);
-
-        function toggleTheme() {
-            const theme = document.documentElement.getAttribute('data-theme');
-            const newTheme = theme === 'light' ? 'dark' : 'light';
-            
-            document.documentElement.setAttribute('data-theme', newTheme);
-            localStorage.setItem('theme', newTheme);
-            
-            // Update icon
-            const icon = document.querySelector('.theme-toggle-slider i');
-            icon.className = newTheme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
-        }
-
         // Helper: Normalize ISBN (remove hyphens/spaces)
         function normalizeIsbn(isbn) {
             return (isbn || '').toString().replace(/[^0-9X]/gi, '').toUpperCase();
@@ -184,12 +169,8 @@
             attemptNext();
         }
 
-        // Set initial icon on page load and resolve book covers
+        // Resolve book covers on page load
         window.addEventListener('DOMContentLoaded', (event) => {
-            const theme = document.documentElement.getAttribute('data-theme');
-            const icon = document.querySelector('.theme-toggle-slider i');
-            if (icon) icon.className = theme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
-
             // Resolve covers with fallbacks/alternates
             document.querySelectorAll('.book-cover img[data-isbn]').forEach(img => {
                 tryLoadCover(img);
diff --git a/index.html b/index.html
index 9b92ccd..35048cf 100644
--- a/index.html
+++ b/index.html
@@ -75,6 +75,7 @@
             font-size: 0.9rem;
         }
     </style>
+    <script src="js/theme.js"></script>
     <script>
         // Check for saved theme preference or default to light mode
         const currentTheme = localStorage.getItem('theme') || 'light';
diff --git a/js/theme.js b/js/theme.js
new file mode 100644
index 0000000..479ed12
--- /dev/null
+++ b/js/theme.js
@@ -0,0 +1,24 @@
+// Theme toggle functionality shared across pages
+
+// Check for saved theme preference or default to light mode
+const currentTheme = localStorage.getItem('theme') || 'light';
+document.documentElement.setAttribute('data-theme', currentTheme);
+
+function toggleTheme() {
+    const theme = document.documentElement.getAttribute('data-theme');
+    const newTheme = theme === 'light' ? 'dark' : 'light';
+    
+    document.documentElement.setAttribute('data-theme', newTheme);
+    localStorage.setItem('theme', newTheme);
+    
+    // Update icon
+    const icon = document.querySelector('.theme-toggle-slider i');
+    icon.className = newTheme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
+}
+
+// Set initial icon on page load
+window.addEventListener('DOMContentLoaded', (event) => {
+    const theme = document.documentElement.getAttribute('data-theme');
+    const icon = document.querySelector('.theme-toggle-slider i');
+    if (icon) icon.className = theme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
+});