Log message when the dark theme cookie can't be read

backend/src/app.rs

@@ -393,7 +393,11 @@ async fn context(
     let tr = Tr::new(&language);
 
     let dark_theme = match jar.get(common::consts::COOKIE_DARK_THEME) {
-        Some(dark_theme_cookie) => dark_theme_cookie.value().parse().unwrap_or_default(),
+        Some(dark_theme_cookie) => dark_theme_cookie
+            .value()
+            .parse()
+            .inspect_err(|err| warn!("Can't parse dark theme cookie: {}", err))
+            .unwrap_or_default(),
         None => false,
     };