Add darken the scrollbars in dark mode.

Author: JimBroad

_content/tour/static/css/app.css

@@ -14,6 +14,7 @@ html, body {
 }
 [data-theme='dark'] body {
     background-color: #2B2D2F;
+    scrollbar-color:#2B2D2F #1d1d1d;
 }
 * {
     outline: none;