Centre Menu Bar

This should work good in normal and smaller viewport.

#access ul.menu { text-align: center; }
#access ul.sub-menu { text-align: left; }
#access ul.menu li { display: inline-block; float:none; }

The code must be used in child theme stylesheet, or Custom CSS plugin, because it works on top of main stylesheet.

Also, there seems to be something in the page that ruins responsive layout in small screen around 400px, probably something in widget or that dots thing in post content.

And the menu text, post/page name should be capitalized by CSS if wanted, but not by itself.