I used two fat quarters and quilted some batting to the outer fabric using straight line stitching about 1" apart.
I attached a black elastic hair tie in between the two fabrics to act as the loop to close the sleeve (see above) and stitched one of my labels on the bag - just so Mr. SDSC knew where it came from! Now, don't look too closely at the stitching, it looks as though my straight line stitching was not very straight!! The button is a standard self covered button - unfortunately this sleeve used up practically all of the fat quarters as I would have liked to have covered the button in one of those two fabrics.
The fold over flap added another 4" to the length of the sleeve - I wanted to keep this an easy project!
Ta da! One happy Mr. SDSC and one protected computer!