Adding logo at the top of the board index page - Adding border around board index

[MGadAllah]

I do not know what is wrong
but since I've tried these codes and I got a strange thing in the admin control panel
each time I go to admin control panel I got an error:
Your IP address does not match the administration session.
and keep log me out
and when I removed all codes you told me about from CSS or the header and make them like it was before I found it still the same error
So please advice