Display issues in Firefox

Hi, we seem to have an issue in Firefox, see screenshot https://www.easysoftwaredeployment.nl/wp-content/uploads/2020/06/esd-firefox-issue.png – how can I fix this?

Also, there is a container that is 150px wide, but if I change this to, say, 500px with the adaption below, it changes the width in the inspection tool in Chrome, but when I add it to my CSS, it has no effect.

@media only screen and (max-width: 1366px)
#eckb-article-body .eckb-article-toc .eckb-article-toc__inner {
width: 500px !important;
middle: -175px !important;
}

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