Board Thread:Support Requests - Getting Technical/@comment-39833655-20190618174336/@comment-9605025-20190618182212

If you haven't already, I would suggest reading Help:Infoboxes, Help:Infoboxes/Tags, and Help:Infoboxes/CSS.

When you say it is just one infobox, do you mean you want to change the width for the infobox on just that one page or that you want to change the width for that type of infobox on all pages?