Board Thread:Support Requests - Designing Your Wiki/@comment-44481222-20200125135635/@comment-9605025-20200125200151

To do that, you will need to use CSS. That is why Tupka217 linked to that page. This is what you currently have. A CSS rule is composed of a selector, an opening brace, one or more property declarations, and a closing brace. You have two rules at the moment. The one that starts with ".portable-infobox" should take care of the rounded corners. The one that starts with ".infobox" will not impact portable infoboxes. Is it meant to?

To change colors based on season, you will need to use infobox themes. In turn, this means you will need to use source mode; as you suspected. If InfoboxBuilder is loaded when you try to edit an infobox, you can access source mode by clicking the button depicting "[]". It should be in the lower-right corner of the editing pane.