This screenshot shows a dynamic container case in the Properties pane and the canvas in the Page Designer.

This image shows the case's Condition field containing an expression, and the three sections that are defined for this case. The case is outlined in orange to indicate Layout Preview is enabled for the case. The cursor is hovering over the Layout Preview button.

The canvas in the Page Designer is in Layout Preview mode, showing how the page looks when the case is displayed in the container.