There are different ways to decorate a Basket. like a Fabric, Plastic Bottle, Colours, Thread and so on. but most of the people used fabric to decorate a Basket.
Place the fabric wrong side up, and the basket bottom with the batting side down. Cut the fabric and leave enough to glue onto the cardboard bottom. Apply glue to the edge of the cardboard and attach the fabric. Flip the bottom piece right side up and place it inside the basket.