Creating a background with two tone but at an angle.

Use the Rectangular Shape tool to make a box with a fill but no stroke. With the Pen tool, click on the middle of the top edge of the Shape. You will see the Pen cursor change to have a little plus sign by it, and a new control point will be added. Now Alt+Click on this point with the Pen tool to convert it to a Corner Point. Finally, hold the Control key to change the Pen to the Direct Selection tool, and drag this point downward.