Unhelpful error shown for invalid login details

[notramo]

Try to log in with an invalid username/password.

The app shows "An error occured" at the bottom with neutral color.

It should make the username and password fields invalid (e.g. error coloring) and show the error message "Invalid username or password". The error message should be placed below the inputs, as it's harder to notice at the bottom of the screen due to change blindness.