Keep Recent Activity nav buttons inside parent div

When the recent activity box is full with longer activities, the nav
buttons can get pushed ouut the bottom of the div because of the height
being set explicitly. Changing to max-height fixes the problem.

dashboard-ui/css/site.css

@@ -822,7 +822,7 @@ progress {
     }
 
         .firstDashboardHomeRightColumn .ui-collapsible-content {
-            height: 585px;
+            min-height: 585px;
         }
 }