fix: change hero background to blue

This edit updates the hero section background color to blue as requested.

Author: Born14

fixtures/demo-app/server.js

@@ -283,3 +283,4 @@ const server = http.createServer((req, res) => {
 server.listen(PORT, () => {
   console.log(`Demo app listening on port ${PORT}`);
 });
+// Agent claims to fix the hero color but uses wrong value