Step 1:
Fill an area with a size of your chioce with glowstone/sea lanterns/torches/another glowing block.

Step 2:
Put walls and a ceiling around the floor.

Step 3:
Fill the area above the light blocks with upside down slabs of your choice.
These are going to be the light blocks.

Step 4:
Replace some of the slabs with full blocks (The same blocks as the slabs)
These are going to be the dark blocks.

Now you have cool floor lighting.

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