Bake and cool 2-layer round cake. Place on foil-wrapped cake circle. Ice smooth with white buttercream.
For candles, use Slide-N-Cut Edge Cutter to cut ten 1 x 2 3/4 in. rectangles from Bright Green and Bright Blue Sugar Sheets! For stripes, use Rotary Cutter to cut 1/4 in. wide strips from Bright Yellow and Red Sugar Sheets! to fit candles. Brush shiny side of stripes with piping gel and attach to contrasting color candles. Use Rotary Cutter to cut 1/8 x 1/4 in. wicks from Black Sugar Sheets! Use punch with 3-star cutting insert from Layered Stars set to cut star flame from Bright Yellow Sugar Sheets. Attach wick and star to candle with piping gel.
For balloons, use punch with large Layered Circle cutting insert to cut rounds from Bright Blue, Red, Bright Yellow and Bright Green Sugar Sheets! For knots, use Rotary Cutter to cut small triangles from matching color Sugar Sheets! Use Rotary Cutter to cut 1/8 in. wide x 2 1/2 in. long strings from Black Sugar Sheets. Attach strings and knots to balloons with piping gel and position on cake top.
For streamers, make curliques using 2 x 1/4 in. wide strips cut from Red and Bright Blue Sugar Sheets! Let dry on cornstarch-dusted board. Position around cake.