Brine family fixed header too wide on Constrained Width

Site URL: https://retronaut.com/home-index

Hi there folks - I have used Brine Sonora for this site. I have added a fixed header plugin to the code injection, and a sidebar.

I want to use constrained width so that index banner images do not pixellate on large monitors. However, when I do this, the header expands beyond the width of the site and window (see attached images). 

The issue is only visible on 'large' monitors,  which show the whole site is constrained, except for the header.  You can see in the attached grab that the header has expanded beyond the window, cutting off the top right social icons.

I could switch to full background - but then the padding of the sidebar vanishes, which is another kind of problem.

If anyone can help me, I will owe them big time...

Wolfgang

.Header {
    left: 0px;
}

BOOM! Done.  That;'s so cool, thank you so much!