Light seeps through gaps in a stair-based roof construction into confined dark spaces

How to Reproduce:

1. Build a roof-like structure using wooden stairs placed laterally on the sides, ensuring there are exposed gaps between the stair blocks without filling them with other blocks (as shown in the first two images).

2. Construct a fully enclosed, unlit, and confined space directly beneath this stair structure (as shown in the last two images).

3. Enter the enclosed room and look at the floor while standing inside it.

Observed Result:
Despite the stairs forming what appears to be a solid barrier from above, ambient light passes through the small gaps and exposed corner spaces between the stair blocks. This significantly illuminates the grass blocks on the floor of the otherwise pitch-black enclosed area below.

Expected:
The solid geometry of the stair blocks should correctly block light rays. The room underneath should remain completely dark since the roof is constructed of solid blocks and there are no direct, open air gaps. Light should not bleed through the partial-block geometry of the stairs in this specific lateral configuration.

Environment / Version:
Minecraft Java Edition (reproduced in a Superflat World, as demonstrated in the attached screenshots).