Step three:

Create a new layer set and a new layer inside the set.

With the pencil tool and foreground color of #000000, draw a 1 px line from one side to another.

Create another layer and draw a 1 px #FFFFFF line below the first line. Merge both layers and set the opacity level to 26%.

3 px below the line you just merge, draw a thin #000000 block but this time dont let it touch the edges.

Duplicate the line layer and position it below the block.

Step four:

Duplicate the layer set and position it below the original, leave some space between them.