Board Thread:Support Requests - Designing Your Wiki/@comment-25714421-20170730144102/@comment-9605025-20170801233126

You can try but I believe MediaWiki (or, at least Wikia) has some bug where in-line use of "background-image" is ignored. So, I don't think it will work. As for transferring the text shadow, there is no "import" capability. You just have to add the relevant CSS to MediaWiki:Common.css. I am assuming you are using a portable infobox. In that case, view Help:Infoboxes/CSS to find the appropriate selector for your CSS. - Edit:

You do not need to use an infobox theme if you want the same text shadowing for all infoboxes.