Better yet, have something that looks like this at the top of the subreddit view: [ Sidebar > ] When the user clicks it, Alien Blue would show the sidebar

Better yet, have something that looks like this at the top of the subreddit view: [ Sidebar > ] When the user clicks it, Alien Blue would show the sidebar. The sidebar view would have this at the top to make it easy to return to the post view: [ < Posts ]