diff --git a/src/wp-content/themes/twentysixteen/css/blocks.css b/src/wp-content/themes/twentysixteen/css/blocks.css
index 47a13e04d9..de6f19fd53 100644
--- a/src/wp-content/themes/twentysixteen/css/blocks.css
+++ b/src/wp-content/themes/twentysixteen/css/blocks.css
@@ -319,6 +319,12 @@ hr.wp-block-separator {
 	margin-bottom: 0;
 }
 
+/* Details */
+
+.wp-block-details > summary:first-of-type {
+	display: list-item;
+}
+
 /*--------------------------------------------------------------
 5.0 Blocks - Widget Blocks
 --------------------------------------------------------------*/
diff --git a/src/wp-content/themes/twentythirteen/css/blocks.css b/src/wp-content/themes/twentythirteen/css/blocks.css
index 092b335d00..5eb588a4a6 100644
--- a/src/wp-content/themes/twentythirteen/css/blocks.css
+++ b/src/wp-content/themes/twentythirteen/css/blocks.css
@@ -544,6 +544,12 @@ body:not(.sidebar) .wp-block-table.alignfull {
 	margin-bottom: 0;
 }
 
+/* Details */
+
+.wp-block-details > summary:first-of-type {
+	display: list-item;
+}
+
 /*--------------------------------------------------------------
 6.0 Blocks - Widgets
 --------------------------------------------------------------*/