Display TOC list inline (horizontally)

I set up my web site a few years ago now in WordPress, and to get the plugin to display how I wanted it to, I had to edit the custom CSS and tweak the php. At the time I knew what I was doing, but I haven’t changed it in 3 years. With the plugin updates, I lost my customisations. I took notes, so I know what I did but now I get CSS errors and I can’t quite recall exactly where I tweaked the php code.

In the CSS I did this:

#toc-np-container {
padding: 0.5em;
margin-bottom: 0.5em;
width: auto;
display: table;
margin: 0 auto;
}

… and also …

#toc-np-container li.header-level-1 {
font-weight: bold;
margin-top: 4px;
display: inline;
}

In the plugin code I also added this:

$items .= ‘ | ‘;

The idea was to display the TOC horizontally like so:

Information | Memories | Packaging | Scrapbook | Data |

Unfortunately, CSS no longer likes margin-top and display: inline and I need to remember where to put my slight code addition so it places a | between each TOC entry.

Either that, or is there a better way of using this plugin to display the TOC horizontally?

Thanks!

The page I need help with: [log in to see the link]