the thin black trim that you would use for fan holes
What you want to do is cut the shape you want in the side of your case but dont cut that same shape out of the lexan. Instead cut the lexan to fit the shape of that side of the case (rectangle). Attach the lexan to the inside of the side with the velcro(you can use silicon as well but I like to use velcro it makes it easier to get off incase I need to change it). From the outside of the case the lexan will look like the shape you cut out. Then put the trim on the edge to finish off the look
