diff --git a/core/misc/vertical-tabs.css b/core/misc/vertical-tabs.css
index f6ae0a2b93e..d61b5917c30 100644
--- a/core/misc/vertical-tabs.css
+++ b/core/misc/vertical-tabs.css
@@ -4,6 +4,7 @@
  */
 
 .vertical-tabs {
+  display: flex;
   margin: 1em 0 1em 15em; /* LTR */
   border: 1px solid #ccc;
 }
diff --git a/core/themes/stable9/css/core/vertical-tabs.css b/core/themes/stable9/css/core/vertical-tabs.css
index f6ae0a2b93e..d61b5917c30 100644
--- a/core/themes/stable9/css/core/vertical-tabs.css
+++ b/core/themes/stable9/css/core/vertical-tabs.css
@@ -4,6 +4,7 @@
  */
 
 .vertical-tabs {
+  display: flex;
   margin: 1em 0 1em 15em; /* LTR */
   border: 1px solid #ccc;
 }