In the 'page settings' tab you can manually set your workspace dimensions and there is a dropdown menu to change the display mode of the page. The display modes are: original, fullscreen, zoom, longpage.
 
Original

This will put the canvas in the center of the screen with a small shadow around it. It will only shrink when a screen is smaller. The size you set will be the maximum size of the canvas. Space surrounding the canvas will be filled with a default color. 

Fullscreen

With this setting you can create a more fullscreen effect because the background and some other elements can be set to fullscreen. The part of the canvas that’s inside the Safe Zones will stay visible at all times and will scale up or down as much as it can while keeping the same ratio. 

Zoom

The zoom setting works almost the same way as the fullscreen setting nothing can be set to fullscreen. There’s a background color that will look fullscreen when it matches the background color of your canvas. 

Longpage

The page will be a set as a long page in which you can scroll up and down to navigate. The width of your canvas is the max width of your elements and background-image. If the screen is wider than the canvas a background-color will appear on the left and right side.