Revert "Stewart: removing no needed separator options"

This reverts commit 5a575918e63f6cceb6fd564d5c452a8b52c66533.

stewart/theme.json

@@ -285,6 +285,8 @@
 			},
 			"core/separator": {
 				"border": {
+					"color": "currentColor",
+					"style": "solid",
 					"width": "0 0 1px 0"
 				}
 			},