Index: src/wp-content/themes/twentysixteen/style.css
===================================================================
--- src/wp-content/themes/twentysixteen/style.css	(revision 61499)
+++ src/wp-content/themes/twentysixteen/style.css	(working copy)
@@ -81,8 +81,7 @@
 main,
 menu,
 nav,
-section,
-summary {
+section {
 	display: block;
 }
 
Index: src/wp-content/themes/twentythirteen/style.css
===================================================================
--- src/wp-content/themes/twentythirteen/style.css	(revision 61499)
+++ src/wp-content/themes/twentythirteen/style.css	(working copy)
@@ -74,8 +74,7 @@
 footer,
 header,
 nav,
-section,
-summary {
+section {
 	display: block;
 }