Visually split login buttons for guest and account
It is confusing to have the input fields first, then the two login buttons of which the second one (the guest account login) doesn't need the input fields. Since a guest account is probably the most common way to use the software (especially since the direct link log you in as guest), i'd suggest a login dialog which represents that. We could e.g. move the guest login button to the top and have a divider to the account form field.