Thank you for your replies.
I cannot remove the log-in. It’s a client website.
I have not yet tried the CSS fixes. I want to do my best to make sure I have identified the correct elements. (Thanks very much for descriving what I need to do. I am not quite a complete newbie, but pretty close.)
I think what I need to modify are:
.site-header
and
.main-header-menu
In one place, the consols shows #masthead.site-header
Does #masthead need to be included?
How will this affect mobile?