Fixed z-index definitions to avoid hiding of tree menus

Change-Id: I71044f36ac9c195341dd38735cd8a4c45ee09a36
diff --git a/dev/scss/header/datepicker.scss b/dev/scss/header/datepicker.scss
index 5386d3c..faf8336 100644
--- a/dev/scss/header/datepicker.scss
+++ b/dev/scss/header/datepicker.scss
@@ -12,7 +12,7 @@
 div.datepicker {
   display: inline-block;
   position: absolute;
-  z-index: 8000;
+  z-index: 90;
 
   font-size: 80%;
   padding: 4pt;