To Start off, make a new Photoshop document with dimensions of 740 width by 440 height. Create new layer and zoom in to 400%. Make a rectangular selection and choose the gradient tool, setting it as a linear gradient. Select light grey (CED2D6) for the foreground and a slightly darker grey (B4B9BF) for the background. Make a gradient in the direction of the red arrow, shown in image a). Create a another layer and make a 2nd gradient, with CBD0D4 for the foreground and EBEEEF for the background. Once you've made the two gradients, zoom back out to normal viewing. Merge the gradient layers together and then choose the transform tool (edit > transform).

Stretch the gradient layer so that it spans from the top of the document to the bottom of it. Next, create a pixel wide dark and light grey line, to the left of the gradient layer.