Vanilla Mobs only spawn on specific blocks

I've been using a plugin called NoSpawn to prevent mobs from spawning over certain block types, however that plugin is no longer working under 1.12.

I'm trying to get the same result with here, where vanilla mobs can only spawn over SmoothStone blocks, preferably only underground, only affecting the main overworld.

I've got the conditions part down, I think, but after looking through the the help guides, I can't seem to find to correct syntax for spawning/despawning under these conditions....

Vanilla Mobs only spawn on specific blocks