diff --git a/web/viewer.css b/web/viewer.css
index 6c7b551e8..040b87bdf 100644
--- a/web/viewer.css
+++ b/web/viewer.css
@@ -8,6 +8,10 @@ body {
   padding: 0px;
 }
 
+[hidden] {
+  display: none;
+}
+
 /* === Toolbar === */
 #controls {
   background-color: #eee;
diff --git a/web/viewer.html b/web/viewer.html
index f761c94fe..4175d29fc 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -82,7 +82,7 @@
         <div id="sidebarScrollView">
           <div id="sidebarView"></div>
         </div>
-        <div id="outlineScrollView" style="display:none">
+        <div id="outlineScrollView" hidden='true'>
           <div id="outlineView"></div>
         </div>
         <div id="sidebarControls">