Many thanks for taking the time to reply to this.

By tweaking your supplied percentage value, I can make the menu seem “centered”. However, the value that centers in Firefox does not produce a centered outcome in Safari. So to make this work, I’d need to have a different value for every possible permutation of browser and screen resolution :(

Is there no way to get this done using something like a left and right “auto” margin, so that the menu element is automatically and mathematically centred, without having to resort to a nudge-from-the-left hack?