Step 1
Open a document and fill it with a dark color. This will be your background. Make a new layer and Draw a rectangle spanning the height of the document. Make the width around 20-30 px wide. Apply a gradient Overlay to this rectangle. Make sure the colors match the background and that the lighter side is facing outwards from the middle of the document.
Step 2
Place this border to the left of the document. Now duplicate it and scale the width down until it fits nicely into the first rectangle. Now double click this layer and change the Gradient Overlay angle so that the lighter side is facing inwards towards the center of the document.
Step 3
Now duplicate these two layers and place them on the right. Inverse the overlay's angles so that the gradients are facing the right directions. The lighter side of the outer gradient needs to be pointing away from the center and vice versa for the inner rectangle.
Final Result:
