Upholstery for the lazy girl! When decorating, always keep in mind that no-one's going to see the bottom/back/inside. This is only one small step up from wrapping a loose piece of cloth over a cushion, but it does keep the cover tidy and in place. So: lay that piece of grey denim you're never going to make a skirt from, face up on the floor. Put the cushion more or less in the middle.
This bay window has 3 separate openings with relatively wide molding between each, If you have enough depth, the roman shades can be mounted inside each window opening. In this case it looks like the windows were too shallow and the shades had to be mounted above the windows. The wide molding between windows covers the gap between the shades.