fix

frontend/src/lib/theme.js

@@ -0,0 +1,20 @@
+const KEY = 'filehost.theme';
+
+export function currentTheme() {
+  return document.documentElement.classList.contains('dark') ? 'dark' : 'light';
+}
+
+export function applyTheme(theme) {
+  document.documentElement.classList.toggle('dark', theme === 'dark');
+  try {
+    localStorage.setItem(KEY, theme);
+  } catch {
+    /* ignore */
+  }
+}
+
+export function toggleTheme() {
+  const next = currentTheme() === 'dark' ? 'light' : 'dark';
+  applyTheme(next);
+  return next;
+}