Here is a screen shot in the Preview and it looks the same when I generate.

I did find another forum posting you were involved in, Peter, that is exactly what I did. The posting is called "TOC turns blue when I edit the logo placeholder on the header in layout.css" dated October 16, 2017 that you provided assistance. Here is the link to the posting: https://forums.adobe.com/message/9885549#9885549
Should I import a new clean layout.css from the Charcoal_Grey layout and just not update the sizing of it? I don't like this solution but thought I would ask. You seemed to get it to work, but I'm not sure how from the other posting. I'd appreciate any suggestions.
At a quick read it looks as if importing a new layout and setting the width first did the trick. I think I would leave your project alone and create a new project with just a few topics and try to get the layout working in that.
If that doesn't work and has the same problem, see the Contact page on my site and send the project as instructed there. Do make sure you include a link to this thread and please do not email the project direct.
I won't be able to look at it today and probably not tomorrow.
See www.grainge.org for free RoboHelp and Authoring information.

@petergrainge