* hide download link before scroll down.

docs/css/doc.css

 /*!
- * ZUI: Document - v1.9.2 - 2020-07-09
+ * ZUI: Document - v1.9.2 - 2021-03-18
  * http://openzui.com
  * GitHub: https://github.com/easysoft/zui.git 
- * Copyright (c) 2020 cnezsoft.com; Licensed MIT
+ * Copyright (c) 2021 cnezsoft.com; Licensed MIT
  */
 
 .colorset {
@@ -2426,11 +2426,7 @@ body {
   opacity: .65;
   }
 #navDownloadLink {
-  filter: alpha(opacity=0);
-  opacity: 0;
-  -webkit-transition: opacity .2s cubic-bezier(.175, .885, .32, 1);
-       -o-transition: opacity .2s cubic-bezier(.175, .885, .32, 1);
-          transition: opacity .2s cubic-bezier(.175, .885, .32, 1);
+  visibility: hidden;
   }
 #navbar {
   padding: 20px 0;
@@ -2487,8 +2483,7 @@ body {
   }
 #navbar .navbar-collapse.in #navDownloadLink,
 #navbar .navbar-collapse.collapsing #navDownloadLink {
-  filter: alpha(opacity=100);
-  opacity: 1;
+  visibility: visible;
   }
 #navbar .navbar-collapse.in:before,
 #navbar .navbar-collapse.collapsing:before {
@@ -4538,8 +4533,7 @@ body.compact-mode.compact-mode-in #navbar .navbar-collapse.collapsing .navbar-na
   display: inline;
   }
 body.compact-mode.compact-mode-in #navDownloadLink {
-  filter: alpha(opacity=100);
-  opacity: 1;
+  visibility: visible;
   }
 body.compact-mode.compact-mode-in #compactTogger {
   top: 1px;

src/less/doc.less

@@ -656,8 +656,7 @@ body {
 }
 
 #navDownloadLink {
-  .transition-fast(opacity);
-  .opacity(0);
+  visibility: hidden;
 }
 
 #navbar {
@@ -702,7 +701,7 @@ body {
     &.in,
     &.collapsing {
       #navDownloadLink {
-        .opacity(1);
+        visibility: visible;
       }
       background-color: #fff;
       margin-top: 10px;
@@ -1985,7 +1984,7 @@ body.compact-mode {
       }
     }
     #navDownloadLink {
-      .opacity(1);
+      visibility: visible;
     }
     #compactTogger {
       .opacity(1);