Horizon UI Theme.

I am looking to do a custom theme with Horizon. I looked some on github etc, but I am noticing on the login screen a "header" bar and I can't see where it's coming from. Even the default theme has it. It looks like something in the class for "login" or maybe it's the "container", I am not a CSS guy, more suited to crayons. Any pointers would be appreciated. Cheers. Knox.