diff --git a/calendar/templates/default/app.css b/calendar/templates/default/app.css
index a8ce2d54bb..77cbce82bb 100644
--- a/calendar/templates/default/app.css
+++ b/calendar/templates/default/app.css
@@ -136,6 +136,7 @@ e.g. the div with class calTimeGrid is generated by the timeGridWidget method of
 	border-right: 1px solid silver;
 	height: 16px;
 	line-height: 16px;
+	z-index: 30;
 }
 .calDayColHeader img {
 	vertical-align: middle;