Revert remove light mode fallback

app.py

@@ -2389,17 +2389,21 @@ ATTRIBUTION_HTML = """
 # ---------------------------------------------------------------------------
 EARLY_THEME_JS = """
 (function() {
-    var url = new URL(window.location.href);
-    var isDark;
-    console.log(window.matchMedia);
-    if (url.searchParams.get('__theme') === 'dark') {
-        isDark = url.searchParams.get('__theme') === 'dark';
-    } else {
-        isDark = !!(window.matchMedia &&
-                        window.matchMedia('(prefers-color-scheme: dark)').matches);
-    }
-    if (isDark) {
-        document.documentElement.classList.add('dark');
+    try {
+        var url = new URL(window.location.href);
+        var isDark;
+        if (url.searchParams.get('__theme') === 'dark') {
+            isDark = url.searchParams.get('__theme') === 'dark';
+        } else {
+            isDark = !!(window.matchMedia &&
+                         window.matchMedia('(prefers-color-scheme: dark)').matches);
+        }
+        if (isDark) {
+            document.documentElement.classList.add('dark');
+        }
+    } catch (e) {
+        // If anything above throws (e.g. matchMedia unavailable), just fall
+        // back to the light-mode default rather than breaking the page.
     }
 })();
 """