Start by creating a rectangle using rectangular shape tool.



Press Ctrl+T. Right click the layer and select warp. Select Bulge from the preset warp shapes on top bar. Apply settings as shown.





Press Ctrl+T. Right click the layer and select rotate 90° CW. Press Ctrl+T again. Right click the layer and select warp. Select Bulge from the preset warp shapes on top bar. Apply settings as shown.





Double click the layer to open layer style window. Apply layer style with the settings shown.



You should now have a faded shape like the one below.