How do I write my own css for the injection and how do I do it in general

Embed the CSS into an SVG whose viewBox attribute is missing. Then, make another SVG whose CSS adds long transitions for the CSS in the first SVG. (what you can usually see on CSS projects is a transition towards Scratch's CSS) For static styles, use a stepping timing function, as using continuous timing functions for the entire page slows down the browser. Add the first SVG as a costume, and surround it with copies of the second SVG in the costume list

You should probably learn CSS before you actually write it, and knowing CSS, you're probably going to have to learn HTML too

Thanks y'all I used my chat gpt skills and my limited css knowledge combined with my html skill and I got through it