I added the same design to the skirt, resulting in this. Now we'll adjust the details.

Duplicate the line layer, just as we did before, and un-check transparent pixel lock on the copied layer. Go to filter→gradient→gauss, make it nice and smooth, then go back and lock transparent pixels.

Fill in with this color, and change the layer from normal to multiply. I've set the layer opacity to 50%. It's really hard to tell, but that adds a subtle line effect.

gradient (gauss) about 3-5 pixels