Below is the Microsoft MakeCode for this project:
You may need to enable to view the content. A static picture is below or you you can see on the Microsoft MakeCode site here. On that site, click the DOWNLOAD button/text. Save it somewhere, you will need that file later.
Make sure that code is how you want it. You can use the MakeCode editor to edit the code, but if you think the Rainbow effect is OK for you, then don't do anything, just download it.