The Stairs will have risers--the part your toe would kick as you walk up. Leaving this area open is a code violation and a strangulation and limb-entrapment danger.

The steps are rounded off, so that foot traffic doesn't leave the middle rounded and the sides square. There is a lip of about 3/4"--any more would place the stair tread in jeopardy of breaking along the grain, and any less would make watermarks in the riser as water runs down it.

Also notice the grippable handrail, with a channel on the inside for your fingers. This should follow the natural course of your feet, including a flattening out at the top and bottom.