diff --git a/modules/system/system.base.css b/modules/system/system.base.css
index a6748de..6225984 100644
--- a/modules/system/system.base.css
+++ b/modules/system/system.base.css
@@ -137,6 +137,10 @@ div.tree-child-horizontal {
 table.sticky-header {
   background-color: #fff;
   margin-top: 0;
+  /* Render sticky table headers above any other (relative) positioned elements,
+     but leave sufficient room for z-indexes in a theme, and lastly try to not
+     conflict with "page-level widgets", such as toolbar. */
+  z-index: 100;
 }
 
 /**