The default view in the 2D window shows the front or outside of pieces. You can change the display in the 2D window to view the back or inside of pieces. This is sometimes referred to as the Inside View.
To view the back or inside:
At the top left of the 2D window, hover over and click to reverse the display and show the inside of the pieces.
Repeat the action to return the 2D window to show the front (outside) of the pieces.
The following image shows how to view the inside of pieces.