reverted:
--- b/core/themes/seven/seven.theme
+++ a/core/themes/seven/seven.theme
@@ -185,7 +185,7 @@
 }
 
 /**
+ * Overrides theme_tablesort_indicator().
- * Overrides tablesort-indicator.html.twig.
  *
  * Uses Seven's image versions, so the arrows show up as black and not gray on
  * gray.