Corkboard card lines are set to the default, but they aren’t showing up either in either the inspector, nor in the corkboard.
I can confirm I have the same issue.
Thanks, we’re in something of a transition stage with various options and settings, so this is a fluke of missing some of the index card themes while still having old settings in the Appearance options. At present then there’s no way to display the index card lines, whoops!