Board Thread:Support Requests - Designing Your Wikia/@comment-26731725-20151120235517

If theme-source answer the theme doesn't exist, it'll pick from theme by default.

An example is: Infobox of alliances. With theme-source, each alliance can have its own style for its infobox. However, not all alliances has a designer. So if the alliance doesn't have its own theme, it'll grab from theme. 