can anyone teach me how to make this kind of topper?? Thank you
This is called royal icing color flow or run out. It is pretty easy but just don't attempt it in humid weather, it will never dry!! When filling in, be sure to thin out the icing. Here is a good tutorial
I would use a tip 2 or 3 for the outline. For the color flow, you can use a bigger tip, or just snip a tiny bit of the end of your bag.
Make sure your outline has crusted before filling in, or it will all just run together. I let mine sit about 30 minutes or so.