Unity gaming question- why won't the cube collide and fall into the floor of the box?

Unity 2017.3.0f3 Personal (64bit) Lab 1.0.unity - Lab 1.0 PC, Mac & Linux Standalone (Personal) Center Local Layers Layout Scene Ga Asset S Services E Hierarchy Create Inspector Shaded Gizmos -Cube (Mesh Filter) Lab 1.0' Main Camera Directional Light Mesh Cube Box Collider box Edit Collider floor side1 side2 side3 side4 Is Trigger Material Center None (Physic Mater do x 0 Cube Size Mesh Renderer Lighting Materials Dynamic Occluded A Rigidbody Mass Drag Angular Drag Use Gravity ls Kinematic Interpolate Collision Detection Discrete constraints 0.05 Project 4 | | * Favorites Assets All Materials All Models All Prefabs 1 1 Mesh Collider Assets Convex Lab 1.0 Is Trigger Cooking Options Material Mesh Mixed None (Physic Mater Cube Default-Material Shader Standard