Board Thread:Support Requests - Getting Technical/@comment-28712089-20200812102412/@comment-45117243-20200812232406

HTML is the language any web page is written. The wikitext code is similar to HTML but not exactly the same, and it's translated into HTML. It's probably the way infoboxes captions work and you can't change it. It has nothing to do with the new platform (UCP).

About the CSS, it seems that you messed it up a bit. I suggest you take it back to the version before today changes and then add only this:

Do not change the CSS of .portable-infobox .pi-image .pi-caption { as this is for the regular caption

Then you'll be able to use the regular caption tag when you don't need a special style inside, and use when you need to style the caption contents.