Hello Guys !

Design page curves in Adobe Photoshop by yourself. You can do it by many ways. I will describe here an easy way to do it.

Draw a box shape using pen tool. Clicking p will select pen tool in photoshop.
Now you can add editing points to it because its not a regular shape but its editable.
Add points by Add anchor point tool beneath to pen tool in its sub menu, at the corner where you want to curve to appear (e.g. slightly near from top right corner and slightly near right side under top right corner).
Select top right corner by Direct selection tool and drag it inwards.
Add gradients at that corner. Two gradients I suggest. One darker one at top and lighter one, beneath dark gradient by Gradient tool. You are done.
Thanks.