Index: src/wp-content/themes/twentyfifteen/css/blocks.css
===================================================================
--- src/wp-content/themes/twentyfifteen/css/blocks.css	(revision 57303)
+++ src/wp-content/themes/twentyfifteen/css/blocks.css	(working copy)
@@ -470,7 +470,7 @@
 	}
 }
 
-/* Seperators */
+/* Separator */
 
 .wp-block-separator {
 	border: 0;
Index: src/wp-content/themes/twentyfifteen/css/editor-blocks.css
===================================================================
--- src/wp-content/themes/twentyfifteen/css/editor-blocks.css	(revision 57303)
+++ src/wp-content/themes/twentyfifteen/css/editor-blocks.css	(working copy)
@@ -806,6 +806,7 @@
 /* Separator */
 
 .wp-block-separator {
+	border: 0;
 	max-width: 100px;
 }