Bake and cool a 2-layer 8-in. round cake. Stack cooled cake layers on foil-covered cake board. Prepare for fondant by lightly icing with buttercream.
Tint white fondant teal; cover cake and smooth.
Roll out neon fondant 1/8 in. thick. Cut circles of various sizes and colors using Cut-Outs and Cutter. Cut out centers of some circles with smaller Cut-Outs for open look. Brush back of circles with damp brush; attach randomly to cake, layering some with 2 or 3 circles. For bottom border, cut circles with medium Cut-Out; attach, positioning half on cake, half on board. For each border circle, cut a circle with small Cut-Out; attach in center of medium circle with damp brush.