diff --git a/IPython/html/static/base/less/flexbox.less b/IPython/html/static/base/less/flexbox.less
index 1975676..60874fc 100644
--- a/IPython/html/static/base/less/flexbox.less
+++ b/IPython/html/static/base/less/flexbox.less
@@ -35,7 +35,7 @@ Browsers not listed, including Safari, are supported via the styling under the
     /* Modern browsers */
     display: flex;
     flex-direction: row;
-    align-items: flex-start;
+    align-items: stretch;
 }
 
 .hbox > * {
@@ -67,7 +67,7 @@ Browsers not listed, including Safari, are supported via the styling under the
     /* Modern browsers */
     display: flex;
     flex-direction: column;
-    align-items: flex-start;
+    align-items: stretch;
 }
 
 .vbox > * {