Board Thread:Support Requests - Getting Technical/@comment-33870323-20180221014958/@comment-31420862-20180221024150

Perhaps turn first design into theme as well? That way, it will apply only to certain infoboxes you want and not effect the second infobox. And, yes, these can be customized with themes the same way as without them. See Infobox themes section at Help:Infoboxes/CSS.