In a multi-layer floor, the graphic display of the lines (or edges) between the floor layers can be controlled through the floor subcategories and by overriding the host layers of the floor.
The Common Edges subcategory specifies the graphic display of the lines between layers in a multi-layer floor. The Interior Edges subcategory is applied to edges between adjacent layers that have the same override style.
You can edit the graphic display of floor subcategories from the Visibility/Graphics dialog. See Overriding Graphic Display of Element Categories. To edit host layers, see Override Cut Line Styles.