Maybe not square but this might be an idea to float lights. easy floating pool lanterns DIY by using Styrofoam squares, poking a dowel rod into each corner of the square, and then putting tissue or wax paper around the rods
Love the soft colour combination and it will be great idea as a centre piece for head table. Other tables without flowers. Can buy this type of vase from Brighten at the flower market. Rustic vase: drill out center of branches & fill with flowers!