diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index cb1df15bbb152..e3154ad84afc5 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -303,7 +303,7 @@ nav.sub {
 	left: 0;
 	top: 0;
 	bottom: 0;
-	overflow: auto;
+	overflow-y: scroll;
 }
 
 /* Improve the scrollbar display on firefox */
diff --git a/src/librustdoc/html/static/css/themes/ayu.css b/src/librustdoc/html/static/css/themes/ayu.css
index ba7fb3b5456a5..91ede47c156b8 100644
--- a/src/librustdoc/html/static/css/themes/ayu.css
+++ b/src/librustdoc/html/static/css/themes/ayu.css
@@ -70,11 +70,11 @@ pre, .rustdoc.source .example-wrap {
 
 /* Improve the scrollbar display on firefox */
 * {
-	scrollbar-color: #5c6773 transparent;
+	scrollbar-color: #5c6773 #24292f;
 }
 
 .sidebar {
-	scrollbar-color: #5c6773 transparent;
+	scrollbar-color: #5c6773 #24292f;
 }
 
 /* Improve the scrollbar display on webkit-based browsers */
diff --git a/src/librustdoc/html/static/css/themes/dark.css b/src/librustdoc/html/static/css/themes/dark.css
index 77ac217e6f41d..74a4fe45a3d1b 100644
--- a/src/librustdoc/html/static/css/themes/dark.css
+++ b/src/librustdoc/html/static/css/themes/dark.css
@@ -44,7 +44,7 @@ pre, .rustdoc.source .example-wrap {
 	scrollbar-color: rgb(64, 65, 67) #717171;
 }
 .sidebar {
-	scrollbar-color: rgba(32,34,37,.6) transparent;
+	scrollbar-color: rgba(32,34,37,.6) #5a5a5a;
 }
 
 /* Improve the scrollbar display on webkit-based browsers */