Then glue the coordinating fabric inside the back cover just as you did for the inside of the front cover.
Now is an extremely fun part. You get to play with buttons. BUTTONS! I love buttons - who doesn't? Choose one that goes with your book. The size really doesn't matter - have fun with it.
Fold the skinny strip into the front cover and stitch the button onto the end. This is your bookmark - just like in those beautiful old novels.