Create a new 1024 x 1024 px document in Adobe Photoshop. Set the Foreground color to #7d7d7d and the Background color to #434343. Pick the Gradient Tool, choose the Foreground to Background gradient fill, and click the Radial Gradient icon.
Then, click and drag from the center of the document to one of the corners to create the background gradient, and duplicate the Background layer.