Remove object lines/boundary lines?

[gmangail]

How can I eliminate the black object boundary lines or lines indicating a slope? Please see attachment. I created the concrete slab by using the Floor option. I have tried everything from adjusting the visibility/graphic line colors to material settings. I am a new user operating in version 2019.

[Steve_Stafford]

Visibility/Graphics > Category: Floors > expand the item > uncheck Interior Edges