Update app.py

app.py

@@ -17,7 +17,7 @@ def show_users():
     return users_df.copy()
 
 def login(username, password):
-    username = username.strip().upper()
+    username = username.strip()
     password = password.strip()
     matched = users_df[(users_df["USERNAME"] == username) & (users_df["PASSWORD"] == password)]
     if not matched.empty: