/help/: Fix mobile scrollbar appearing incorrectly.

For <1000px (aka the mobile view), we need to set "overflow: hidden"
on the sidebar unless the sidebar is actually expanded.

Fixes: #6730.

static/styles/portico.css

@@ -1343,13 +1343,14 @@ input.new-organization-button {
         padding-right: 80px;
         transform: translateX(0);
         transition: all 0.3s ease;
-
+        overflow: hidden;
         height: 100vh;
     }
 
     .app.help .sidebar.show {
         padding-right: 20px;
         transform: translateX(280px);
+        overflow: auto !important;
     }
 
     .app.help .sidebar.show + .hamburger {