There is just one Setting:
Allow Hover Previews while moving your Pointer over a Thumbnail or not, this will show a larger Preview next to the Sidebar overlaying the current Page, if you leave a Thumbnail or the Sidebar the Preview gets hidden as well.
In the Sidebar you can see a Button on the very top to toggle the Side of the Sidebar, it can either be on the left or on the right side, it slides away by default leaving a small part visible in the center of the screen, once you hover over it it slides open to show its content, this done to allow you accessing Page content below the Sidebar if there is any.
