Draw a dark rectangle and make it the first layer.
On another layer draw a Polygon. Then use Control+C to copy it and Control+F to paste in front. Using the Shift key you can reduce the size. Change the colour of the image and do the same process again.
Make duplicate copies of various sizes.
Apply drop shadow to the pieces.
Draw a dark brown rectangle over the polygons. Make changes to the opacity to 37% and transparency to Overlay.
Make a copy of one of the polygon. Create a new layer. Lock the other layers.
Paste the polygon and duplicate it. Then resize.
Draw a rectangle with a pixel or two less than the background. Unlock the entire layer and select everything.
Apply Clipping Mask.
This is the result. You can use this simple background for various purposes.