The Sidebar is hidden for screens with width < 870px.  This makes the main page content more readable on small devices, but blocks access to some important links, such as the Login link.
This cookbook shows how to add a button that will toggle the sidebar when it is hidden on  small screen.
This button is configured in any of 
SitePreferences, in 
WebPreferences (for a single web), in your 
WikiGuest topic, or on a single page.
This line loads the extra style definition:
   * Set USERSTYLEURL = %PUBURLPATH{topic="%SYSTEMWEB%.PatternSkinCssCookbookSidebarToggle" "SidebarToggle.css"}%
To activate the button in the sidebar, override the 
viewsidebar.pattern.tmpl using the supplied 
viewsidebar.sidetoggle.tmpl by adding it to the front of
the SKIN setting. 
Your current SKIN setting is 
natedit,pattern
Change it to
    * Set SKIN=sidetoggle,natedit,pattern 
The formating and positioning is done in the css. When the sidebar is hidden, the button will appear in the lower left corner of the screen, appearing as the "hamburg" icon: ... 
.