This is a problem with many skins for Jellyfin, in that there is not consideration for playlist support. In the current implementation of the skin, playlists are listed in a grid, which makes them difficult to read and impossible to modify via the drag-and-drop handles that are part of the playlist interface.
To fix this, I can disable display:grid for #itemDetailPage .vertical-list in the document inspector. However, that then messes up the normal display of episodes in a TV show season.
I think the basic problem is that TV show episode layout and playlist layouts are too similar and its not easy to find a CSS definition that applies to one and not the other.