-/* The slide should be positioned w.r.t. to the canvas.
- The canvas takes up the whole window in screen mode and a
- whole page in print mode
+/* Slide layout
+ .sws-{header,inner-canvas,footer} are in
+ a .sws-canvas which fills the whole viewport vertically
+ and is horizontally centered.
+ The .sws-canvas has an aspect ratio of 4/3 or 16/9